diff --git a/package.json b/package.json
index 2e8445521b0a0..47514e3ec2d3a 100644
--- a/package.json
+++ b/package.json
@@ -63,7 +63,7 @@
     "eslint-plugin-react-internal": "link:./scripts/eslint-rules",
     "fbjs-scripts": "1.2.0",
     "filesize": "^6.0.1",
-    "flow-bin": "0.97",
+    "flow-bin": "^0.122",
     "glob": "^7.1.6",
     "glob-stream": "^6.1.0",
     "google-closure-compiler": "^20200517.0.0",
diff --git a/packages/jest-react/src/internalAct.js b/packages/jest-react/src/internalAct.js
index 4e41f6234c928..a5a398b7e2a0d 100644
--- a/packages/jest-react/src/internalAct.js
+++ b/packages/jest-react/src/internalAct.js
@@ -28,6 +28,8 @@ export function act<T>(scope: () => Thenable<T> | T): Thenable<T> {
       'This version of `act` requires a special mock build of Scheduler.',
     );
   }
+
+  // $FlowFixMe: _isMockFunction doesn't exist on function
   if (setTimeout._isMockFunction !== true) {
     throw Error(
       "This version of `act` requires Jest's timer mocks " +
diff --git a/packages/react-debug-tools/src/ReactDebugHooks.js b/packages/react-debug-tools/src/ReactDebugHooks.js
index 940873725cb2f..7cfb576fad378 100644
--- a/packages/react-debug-tools/src/ReactDebugHooks.js
+++ b/packages/react-debug-tools/src/ReactDebugHooks.js
@@ -683,6 +683,7 @@ function handleRenderFunctionError(error: any): void {
   // TODO: refactor this if we ever combine the devtools and debug tools packages
   wrapperError.name = 'ReactDebugToolsRenderError';
   // this stage-4 proposal is not supported by all environments yet.
+  // $FlowFixMe Flow doesn't have this type yet.
   wrapperError.cause = error;
   throw wrapperError;
 }
diff --git a/packages/react-devtools-shared/src/backend/StyleX/utils.js b/packages/react-devtools-shared/src/backend/StyleX/utils.js
index 68bda23a2262c..2167321b0c84d 100644
--- a/packages/react-devtools-shared/src/backend/StyleX/utils.js
+++ b/packages/react-devtools-shared/src/backend/StyleX/utils.js
@@ -92,7 +92,9 @@ function getPropertyValueForStyleName(styleName: string): string | null {
     ]: any): CSSStyleSheet);
     // $FlowFixMe Flow doesn't konw about these properties
     const rules = styleSheet.rules || styleSheet.cssRules;
+    // $FlowFixMe `rules` is mixed
     for (let ruleIndex = 0; ruleIndex < rules.length; ruleIndex++) {
+      // $FlowFixMe `rules` is mixed
       const rule = rules[ruleIndex];
       // $FlowFixMe Flow doesn't konw about these properties
       const {cssText, selectorText, style} = rule;
diff --git a/packages/react-devtools-shared/src/backend/renderer.js b/packages/react-devtools-shared/src/backend/renderer.js
index 3a893060da0ad..9802d4b8c03d9 100644
--- a/packages/react-devtools-shared/src/backend/renderer.js
+++ b/packages/react-devtools-shared/src/backend/renderer.js
@@ -124,7 +124,7 @@ import type {
 } from 'react-devtools-shared/src/types';
 
 type getDisplayNameForFiberType = (fiber: Fiber) => string | null;
-type getTypeSymbolType = (type: any) => Symbol | number;
+type getTypeSymbolType = (type: any) => symbol | number;
 
 type ReactPriorityLevelsType = {|
   ImmediatePriority: number,
@@ -382,13 +382,14 @@ export function getInternalReactConstants(
   // End of copied code.
   // **********************************************************
 
-  function getTypeSymbol(type: any): Symbol | number {
+  function getTypeSymbol(type: any): symbol | number {
     const symbolOrNumber =
       typeof type === 'object' && type !== null ? type.$$typeof : type;
 
     // $FlowFixMe Flow doesn't know about typeof "symbol"
     return typeof symbolOrNumber === 'symbol'
-      ? symbolOrNumber.toString()
+      ? // $FlowFixMe `toString()` doesn't match the type signature?
+        symbolOrNumber.toString()
       : symbolOrNumber;
   }
 
diff --git a/packages/react-devtools-shared/src/backend/types.js b/packages/react-devtools-shared/src/backend/types.js
index 81ed15b04ae78..be71a816d6327 100644
--- a/packages/react-devtools-shared/src/backend/types.js
+++ b/packages/react-devtools-shared/src/backend/types.js
@@ -84,7 +84,7 @@ export type GetFiberIDForNative = (
 export type FindNativeNodesForFiberID = (id: number) => ?Array<NativeType>;
 
 export type ReactProviderType<T> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   _context: ReactContext<T>,
   ...
 };
diff --git a/packages/react-devtools-shared/src/devtools/views/Button.js b/packages/react-devtools-shared/src/devtools/views/Button.js
index 82400bb8982a2..bdd84b57da431 100644
--- a/packages/react-devtools-shared/src/devtools/views/Button.js
+++ b/packages/react-devtools-shared/src/devtools/views/Button.js
@@ -28,6 +28,7 @@ export default function Button({
   ...rest
 }: Props) {
   let button = (
+    // $FlowFixMe unsafe spread
     <button
       className={`${styles.Button} ${className}`}
       data-testname={testName}
diff --git a/packages/react-devtools-shared/src/devtools/views/Components/NativeStyleEditor/AutoSizeInput.js b/packages/react-devtools-shared/src/devtools/views/Components/NativeStyleEditor/AutoSizeInput.js
index 48c6f304275c7..c8154c6877b98 100644
--- a/packages/react-devtools-shared/src/devtools/views/Components/NativeStyleEditor/AutoSizeInput.js
+++ b/packages/react-devtools-shared/src/devtools/views/Components/NativeStyleEditor/AutoSizeInput.js
@@ -42,6 +42,7 @@ export default function AutoSizeInput({
   const isEmpty = value === '' || value === '""';
 
   return (
+    // $FlowFixMe unsafe rest spread
     <input
       className={[styles.Input, className].join(' ')}
       data-testname={testName}
diff --git a/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/menu-button.js b/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/menu-button.js
index cee8021a191f3..ca93ac41d9d1b 100644
--- a/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/menu-button.js
+++ b/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/menu-button.js
@@ -19,6 +19,7 @@ import useThemeStyles from '../../useThemeStyles';
 const MenuList = ({children, ...props}: {children: React$Node, ...}) => {
   const style = useThemeStyles();
   return (
+    // $FlowFixMe unsafe spread
     <ReachMenuList style={style} {...props}>
       {children}
     </ReachMenuList>
diff --git a/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/tooltip.js b/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/tooltip.js
index d3f07258c8b5b..c6dbec7ff4528 100644
--- a/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/tooltip.js
+++ b/packages/react-devtools-shared/src/devtools/views/Components/reach-ui/tooltip.js
@@ -23,6 +23,7 @@ const Tooltip = ({
 }) => {
   const style = useThemeStyles();
   return (
+    // $FlowFixMe unsafe spread
     <ReachTooltip
       className={`${tooltipStyles.Tooltip} ${className}`}
       style={style}
diff --git a/packages/react-devtools-shared/src/hydration.js b/packages/react-devtools-shared/src/hydration.js
index 0b936462d5fe2..770b168e4b11f 100644
--- a/packages/react-devtools-shared/src/hydration.js
+++ b/packages/react-devtools-shared/src/hydration.js
@@ -396,7 +396,7 @@ export function hydrate(
       parent[last] = undefined;
     } else {
       // Replace the string keys with Symbols so they're non-enumerable.
-      const replaced: {[key: Symbol]: boolean | string, ...} = {};
+      const replaced: {[key: symbol]: boolean | string, ...} = {};
       replaced[meta.inspectable] = !!value.inspectable;
       replaced[meta.inspected] = false;
       replaced[meta.name] = value.name;
diff --git a/packages/react-devtools-shared/src/node_modules/react-window/src/createGridComponent.js b/packages/react-devtools-shared/src/node_modules/react-window/src/createGridComponent.js
index 12d1a4cc9ebd6..8f00a7929dc24 100644
--- a/packages/react-devtools-shared/src/node_modules/react-window/src/createGridComponent.js
+++ b/packages/react-devtools-shared/src/node_modules/react-window/src/createGridComponent.js
@@ -613,6 +613,7 @@ export default function createGridComponent({
       } else {
         itemStyleCache[key] = style = {
           position: 'absolute',
+          // $FlowFixMe computed properties are unsupported
           [direction === 'rtl' ? 'right' : 'left']: getColumnOffset(
             this.props,
             columnIndex,
diff --git a/packages/react-devtools-shared/src/node_modules/react-window/src/createListComponent.js b/packages/react-devtools-shared/src/node_modules/react-window/src/createListComponent.js
index bf9c3e902a96f..6fb6f2d540a21 100644
--- a/packages/react-devtools-shared/src/node_modules/react-window/src/createListComponent.js
+++ b/packages/react-devtools-shared/src/node_modules/react-window/src/createListComponent.js
@@ -469,6 +469,7 @@ export default function createListComponent({
 
         itemStyleCache[index] = style = {
           position: 'absolute',
+          // $FlowFixMe computed properties are unsupported
           [direction === 'rtl' ? 'right' : 'left']: isHorizontal ? offset : 0,
           top: !isHorizontal ? offset : 0,
           height: !isHorizontal ? size : '100%',
diff --git a/packages/react-devtools-shared/src/registerDevToolsEventLogger.js b/packages/react-devtools-shared/src/registerDevToolsEventLogger.js
index 5e1aeba0cd639..fffe07bad7c90 100644
--- a/packages/react-devtools-shared/src/registerDevToolsEventLogger.js
+++ b/packages/react-devtools-shared/src/registerDevToolsEventLogger.js
@@ -31,6 +31,7 @@ export function registerDevToolsEventLogger(
         let metadata = null;
         if (event.metadata != null) {
           metadata = event.metadata;
+          // $FlowFixMe: metadata is not writable and nullable
           delete event.metadata;
         }
         loggingIFrame.contentWindow.postMessage(
@@ -42,7 +43,8 @@ export function registerDevToolsEventLogger(
               version: process.env.DEVTOOLS_VERSION,
               metadata: metadata !== null ? JSON.stringify(metadata) : '',
               ...(fetchAdditionalContext != null
-                ? await fetchAdditionalContext()
+                ? // $FlowFixMe
+                  await fetchAdditionalContext()
                 : {}),
             },
           },
diff --git a/packages/react-devtools-shared/src/utils.js b/packages/react-devtools-shared/src/utils.js
index 2c60fc124e004..1f4582026318d 100644
--- a/packages/react-devtools-shared/src/utils.js
+++ b/packages/react-devtools-shared/src/utils.js
@@ -67,8 +67,8 @@ const encodedStringCache: LRUCache<string, Array<number>> = new LRU({
 });
 
 export function alphaSortKeys(
-  a: string | number | Symbol,
-  b: string | number | Symbol,
+  a: string | number | symbol,
+  b: string | number | symbol,
 ): number {
   if (a.toString() > b.toString()) {
     return 1;
@@ -81,7 +81,7 @@ export function alphaSortKeys(
 
 export function getAllEnumerableKeys(
   obj: Object,
-): Set<string | number | Symbol> {
+): Set<string | number | symbol> {
   const keys = new Set();
   let current = obj;
   while (current != null) {
diff --git a/packages/react-dom/src/events/SyntheticEvent.js b/packages/react-dom/src/events/SyntheticEvent.js
index 3609e6794a50d..2c61b9a42ec23 100644
--- a/packages/react-dom/src/events/SyntheticEvent.js
+++ b/packages/react-dom/src/events/SyntheticEvent.js
@@ -166,7 +166,9 @@ let lastMouseEvent;
 function updateMouseMovementPolyfillState(event) {
   if (event !== lastMouseEvent) {
     if (lastMouseEvent && event.type === 'mousemove') {
+      // $FlowFixMe assuming this is a number
       lastMovementX = event.screenX - lastMouseEvent.screenX;
+      // $FlowFixMe assuming this is a number
       lastMovementY = event.screenY - lastMouseEvent.screenY;
     } else {
       lastMovementX = 0;
@@ -367,7 +369,9 @@ function getEventKey(nativeEvent) {
 
     // FireFox implements `key` but returns `MozPrintableKey` for all
     // printable characters (normalized to `Unidentified`), ignore it.
-    const key = normalizeKey[nativeEvent.key] || nativeEvent.key;
+    const key =
+      // $FlowFixMe unable to index with a `mixed` value
+      normalizeKey[nativeEvent.key] || nativeEvent.key;
     if (key !== 'Unidentified') {
       return key;
     }
@@ -375,7 +379,10 @@ function getEventKey(nativeEvent) {
 
   // Browser does not implement `key`, polyfill as much of it as we can.
   if (nativeEvent.type === 'keypress') {
-    const charCode = getEventCharCode(nativeEvent);
+    const charCode = getEventCharCode(
+      // $FlowFixMe unable to narrow to `KeyboardEvent`
+      nativeEvent,
+    );
 
     // The enter-key is technically both printable and non-printable and can
     // thus be captured by `keypress`, no other non-printable key should.
@@ -384,6 +391,7 @@ function getEventKey(nativeEvent) {
   if (nativeEvent.type === 'keydown' || nativeEvent.type === 'keyup') {
     // While user keyboard layout determines the actual meaning of each
     // `keyCode` value, almost all function keys have a universal value.
+    // $FlowFixMe unable to index with a `mixed` value
     return translateToKey[nativeEvent.keyCode] || 'Unidentified';
   }
   return '';
@@ -441,7 +449,10 @@ const KeyboardEventInterface = {
     // KeyPress is deprecated, but its replacement is not yet final and not
     // implemented in any major browser. Only KeyPress has charCode.
     if (event.type === 'keypress') {
-      return getEventCharCode(event);
+      return getEventCharCode(
+        // $FlowFixMe unable to narrow to `KeyboardEvent`
+        event,
+      );
     }
     return 0;
   },
@@ -462,7 +473,10 @@ const KeyboardEventInterface = {
     // `which` is an alias for either `keyCode` or `charCode` depending on the
     // type of the event.
     if (event.type === 'keypress') {
-      return getEventCharCode(event);
+      return getEventCharCode(
+        // $FlowFixMe unable to narrow to `KeyboardEvent`
+        event,
+      );
     }
     if (event.type === 'keydown' || event.type === 'keyup') {
       return event.keyCode;
@@ -538,7 +552,8 @@ const WheelEventInterface = {
       ? event.deltaX
       : // Fallback to `wheelDeltaX` for Webkit and normalize (right is positive).
       'wheelDeltaX' in event
-      ? -event.wheelDeltaX
+      ? // $FlowFixMe assuming this is a number
+        -event.wheelDeltaX
       : 0;
   },
   deltaY(event) {
@@ -546,10 +561,12 @@ const WheelEventInterface = {
       ? event.deltaY
       : // Fallback to `wheelDeltaY` for Webkit and normalize (down is positive).
       'wheelDeltaY' in event
-      ? -event.wheelDeltaY
+      ? // $FlowFixMe assuming this is a number
+        -event.wheelDeltaY
       : // Fallback to `wheelDelta` for IE<9 and normalize (down is positive).
       'wheelDelta' in event
-      ? -event.wheelDelta
+      ? // $FlowFixMe assuming this is a number
+        -event.wheelDelta
       : 0;
   },
   deltaZ: 0,
diff --git a/packages/react-dom/src/server/ReactDOMFizzServerBrowser.js b/packages/react-dom/src/server/ReactDOMFizzServerBrowser.js
index 2f626c922aa1a..25920232e8710 100644
--- a/packages/react-dom/src/server/ReactDOMFizzServerBrowser.js
+++ b/packages/react-dom/src/server/ReactDOMFizzServerBrowser.js
@@ -57,10 +57,10 @@ function renderToReadableStream(
       const stream: ReactDOMServerReadableStream = (new ReadableStream(
         {
           type: 'bytes',
-          pull(controller) {
+          pull(controller): ?Promise<void> {
             startFlowing(request, controller);
           },
-          cancel(reason) {
+          cancel(reason): ?Promise<void> {
             abort(request);
           },
         },
diff --git a/packages/react-dom/src/server/ReactDOMFizzStaticBrowser.js b/packages/react-dom/src/server/ReactDOMFizzStaticBrowser.js
index 38e4c948f6b9b..c2c619046dff1 100644
--- a/packages/react-dom/src/server/ReactDOMFizzStaticBrowser.js
+++ b/packages/react-dom/src/server/ReactDOMFizzStaticBrowser.js
@@ -50,7 +50,7 @@ function prerender(
       const stream = new ReadableStream(
         {
           type: 'bytes',
-          pull(controller) {
+          pull(controller): ?Promise<void> {
             startFlowing(request, controller);
           },
         },
diff --git a/packages/react-fetch/src/ReactFetchNode.js b/packages/react-fetch/src/ReactFetchNode.js
index 2b1ef5f200cb1..9020529d440d3 100644
--- a/packages/react-fetch/src/ReactFetchNode.js
+++ b/packages/react-fetch/src/ReactFetchNode.js
@@ -43,6 +43,7 @@ function nodeFetch(
     // TODO: cherry-pick supported user-passed options.
   };
   const nodeImpl = protocol === 'https:' ? https : http;
+  // $FlowFixMe: node flow type has `port` as a number
   const request = nodeImpl.request(nodeOptions, response => {
     // TODO: support redirects.
     onResolve(new Response(response));
diff --git a/packages/react-native-renderer/src/legacy-events/accumulateInto.js b/packages/react-native-renderer/src/legacy-events/accumulateInto.js
index 974c0143a5504..7c9f17a757793 100644
--- a/packages/react-native-renderer/src/legacy-events/accumulateInto.js
+++ b/packages/react-native-renderer/src/legacy-events/accumulateInto.js
@@ -40,9 +40,11 @@ function accumulateInto<T>(
   // certain that x is an Array (x could be a string with concat method).
   if (isArray(current)) {
     if (isArray(next)) {
+      // $FlowFixMe `isArray` does not ensure array is mutable
       current.push.apply(current, next);
       return current;
     }
+    // $FlowFixMe `isArray` does not ensure array is mutable
     current.push(next);
     return current;
   }
diff --git a/packages/react-noop-renderer/src/ReactNoopFlightServer.js b/packages/react-noop-renderer/src/ReactNoopFlightServer.js
index 3a84a06d0843c..bd0badc535a8e 100644
--- a/packages/react-noop-renderer/src/ReactNoopFlightServer.js
+++ b/packages/react-noop-renderer/src/ReactNoopFlightServer.js
@@ -53,7 +53,7 @@ const ReactNoopFlightServer = ReactFlightServer({
   },
   resolveModuleMetaData(
     config: void,
-    reference: {$$typeof: Symbol, value: any},
+    reference: {$$typeof: symbol, value: any},
   ) {
     return saveModule(reference.value);
   },
diff --git a/packages/react-reconciler/src/ReactChildFiber.new.js b/packages/react-reconciler/src/ReactChildFiber.new.js
index 71971c03892ca..2e1a232e028db 100644
--- a/packages/react-reconciler/src/ReactChildFiber.new.js
+++ b/packages/react-reconciler/src/ReactChildFiber.new.js
@@ -80,6 +80,7 @@ if (__DEV__) {
       );
     }
 
+    // $FlowFixMe unable to narrow type from mixed to writable object
     child._store.validated = true;
 
     const componentName = getComponentNameFromFiber(returnFiber) || 'Component';
diff --git a/packages/react-reconciler/src/ReactChildFiber.old.js b/packages/react-reconciler/src/ReactChildFiber.old.js
index 86f75fbf65ea8..c6fdbcc728a29 100644
--- a/packages/react-reconciler/src/ReactChildFiber.old.js
+++ b/packages/react-reconciler/src/ReactChildFiber.old.js
@@ -80,6 +80,7 @@ if (__DEV__) {
       );
     }
 
+    // $FlowFixMe unable to narrow type from mixed to writable object
     child._store.validated = true;
 
     const componentName = getComponentNameFromFiber(returnFiber) || 'Component';
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.new.js b/packages/react-reconciler/src/ReactFiberCommitWork.new.js
index d2cd313a05ac8..c70e4ae3470e7 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.new.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.new.js
@@ -296,6 +296,7 @@ function safelyDetachRef(current: Fiber, nearestMountedAncestor: Fiber | null) {
         }
       }
     } else {
+      // $FlowFixMe unable to narrow type to RefObject
       ref.current = null;
     }
   }
@@ -1522,6 +1523,7 @@ function commitAttachRef(finishedWork: Fiber) {
         }
       }
 
+      // $FlowFixMe unable to narrow type to the non-function case
       ref.current = instanceToUse;
     }
   }
@@ -1542,6 +1544,7 @@ function commitDetachRef(current: Fiber) {
         currentRef(null);
       }
     } else {
+      // $FlowFixMe unable to narrow type to the non-function case
       currentRef.current = null;
     }
   }
diff --git a/packages/react-reconciler/src/ReactFiberCommitWork.old.js b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
index 70a68617763c3..4b5076a61c51f 100644
--- a/packages/react-reconciler/src/ReactFiberCommitWork.old.js
+++ b/packages/react-reconciler/src/ReactFiberCommitWork.old.js
@@ -296,6 +296,7 @@ function safelyDetachRef(current: Fiber, nearestMountedAncestor: Fiber | null) {
         }
       }
     } else {
+      // $FlowFixMe unable to narrow type to RefObject
       ref.current = null;
     }
   }
@@ -1522,6 +1523,7 @@ function commitAttachRef(finishedWork: Fiber) {
         }
       }
 
+      // $FlowFixMe unable to narrow type to the non-function case
       ref.current = instanceToUse;
     }
   }
@@ -1542,6 +1544,7 @@ function commitDetachRef(current: Fiber) {
         currentRef(null);
       }
     } else {
+      // $FlowFixMe unable to narrow type to the non-function case
       currentRef.current = null;
     }
   }
diff --git a/packages/react-reconciler/src/ReactFiberHotReloading.new.js b/packages/react-reconciler/src/ReactFiberHotReloading.new.js
index 22b78280f9cba..469fbabf9ed2f 100644
--- a/packages/react-reconciler/src/ReactFiberHotReloading.new.js
+++ b/packages/react-reconciler/src/ReactFiberHotReloading.new.js
@@ -222,6 +222,7 @@ export function markFailedErrorBoundaryForHotReloading(fiber: Fiber) {
       return;
     }
     if (failedBoundaries === null) {
+      // $FlowFixMe Flow got confused by the feature check above.
       failedBoundaries = new WeakSet();
     }
     failedBoundaries.add(fiber);
diff --git a/packages/react-reconciler/src/ReactFiberHotReloading.old.js b/packages/react-reconciler/src/ReactFiberHotReloading.old.js
index 805176560c4bc..c503c7a111212 100644
--- a/packages/react-reconciler/src/ReactFiberHotReloading.old.js
+++ b/packages/react-reconciler/src/ReactFiberHotReloading.old.js
@@ -222,6 +222,7 @@ export function markFailedErrorBoundaryForHotReloading(fiber: Fiber) {
       return;
     }
     if (failedBoundaries === null) {
+      // $FlowFixMe Flow got confused by the feature check above.
       failedBoundaries = new WeakSet();
     }
     failedBoundaries.add(fiber);
diff --git a/packages/react-reconciler/src/ReactTestSelectors.js b/packages/react-reconciler/src/ReactTestSelectors.js
index adadc8ed73e80..ad1333c936147 100644
--- a/packages/react-reconciler/src/ReactTestSelectors.js
+++ b/packages/react-reconciler/src/ReactTestSelectors.js
@@ -39,7 +39,7 @@ if (typeof Symbol === 'function' && Symbol.for) {
   TEXT_TYPE = symbolFor('selector.text');
 }
 
-type Type = Symbol | number;
+type Type = symbol | number;
 
 type ComponentSelector = {|
   $$typeof: Type,
diff --git a/packages/react-server-dom-webpack/src/ReactFlightDOMServerBrowser.js b/packages/react-server-dom-webpack/src/ReactFlightDOMServerBrowser.js
index 93d047e4a0439..2cbd609b473f2 100644
--- a/packages/react-server-dom-webpack/src/ReactFlightDOMServerBrowser.js
+++ b/packages/react-server-dom-webpack/src/ReactFlightDOMServerBrowser.js
@@ -52,13 +52,13 @@ function renderToReadableStream(
   const stream = new ReadableStream(
     {
       type: 'bytes',
-      start(controller) {
+      start(controller): ?Promise<void> {
         startWork(request);
       },
-      pull(controller) {
+      pull(controller): ?Promise<void> {
         startFlowing(request, controller);
       },
-      cancel(reason) {},
+      cancel(reason): ?Promise<void> {},
     },
     // $FlowFixMe size() methods are not allowed on byte streams.
     {highWaterMark: 0},
diff --git a/packages/react-server-dom-webpack/src/ReactFlightServerWebpackBundlerConfig.js b/packages/react-server-dom-webpack/src/ReactFlightServerWebpackBundlerConfig.js
index caeed14a7b7b1..8d7dccae333f2 100644
--- a/packages/react-server-dom-webpack/src/ReactFlightServerWebpackBundlerConfig.js
+++ b/packages/react-server-dom-webpack/src/ReactFlightServerWebpackBundlerConfig.js
@@ -17,7 +17,7 @@ export type BundlerConfig = WebpackMap;
 
 // eslint-disable-next-line no-unused-vars
 export type ModuleReference<T> = {
-  $$typeof: Symbol,
+  $$typeof: symbol,
   filepath: string,
   name: string,
   async: boolean,
diff --git a/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js b/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
index 0c49d293733c5..b3da107e60b9c 100644
--- a/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
+++ b/packages/react-server-dom-webpack/src/ReactFlightWebpackPlugin.js
@@ -25,7 +25,7 @@ import {
 import isArray from 'shared/isArray';
 
 class ClientReferenceDependency extends ModuleDependency {
-  constructor(request) {
+  constructor(request: mixed) {
     super(request);
   }
 
diff --git a/packages/react-server/src/ReactFlightServer.js b/packages/react-server/src/ReactFlightServer.js
index 7c6801e378754..1e84a89350c09 100644
--- a/packages/react-server/src/ReactFlightServer.js
+++ b/packages/react-server/src/ReactFlightServer.js
@@ -86,6 +86,7 @@ export type ReactModel =
   | string
   | boolean
   | number
+  | symbol
   | null
   | Iterable<ReactModel>
   | ReactModelObject;
@@ -119,7 +120,7 @@ export type Request = {
   completedModuleChunks: Array<Chunk>,
   completedJSONChunks: Array<Chunk>,
   completedErrorChunks: Array<Chunk>,
-  writtenSymbols: Map<Symbol, number>,
+  writtenSymbols: Map<symbol, number>,
   writtenModules: Map<ModuleKey, number>,
   writtenProviders: Map<string, number>,
   identifierPrefix: string,
@@ -746,12 +747,17 @@ export function resolveModelToJSON(
     if (existingId !== undefined) {
       return serializeByValueID(existingId);
     }
-    const name = value.description;
+    // $FlowFixMe `description` might be undefined
+    const name: string = value.description;
 
+    // $FlowFixMe `name` might be undefined
     if (Symbol.for(name) !== value) {
       throw new Error(
         'Only global symbols received from Symbol.for(...) can be passed to client components. ' +
-          `The symbol Symbol.for(${value.description}) cannot be found among global symbols. ` +
+          `The symbol Symbol.for(${
+            // $FlowFixMe `description` might be undefined
+            value.description
+          }) cannot be found among global symbols. ` +
           `Remove ${describeKeyForErrorMessage(
             key,
           )} from this object, or avoid the entire object: ${describeObjectForErrorMessage(
diff --git a/packages/react-server/src/ReactFlightServerConfigStream.js b/packages/react-server/src/ReactFlightServerConfigStream.js
index b9772ef6f2ea9..6320f28d585b6 100644
--- a/packages/react-server/src/ReactFlightServerConfigStream.js
+++ b/packages/react-server/src/ReactFlightServerConfigStream.js
@@ -94,7 +94,8 @@ export function processModelChunk(
   id: number,
   model: ReactModel,
 ): Chunk {
-  const json = stringify(model, request.toJSON);
+  // $FlowFixMe: `json` might be `undefined` when model is a symbol.
+  const json: string = stringify(model, request.toJSON);
   const row = serializeRowHeader('J', id) + json + '\n';
   return stringToChunk(row);
 }
@@ -114,7 +115,8 @@ export function processModuleChunk(
   id: number,
   moduleMetaData: ReactModel,
 ): Chunk {
-  const json = stringify(moduleMetaData);
+  // $FlowFixMe: `json` might be `undefined` when moduleMetaData is a symbol.
+  const json: string = stringify(moduleMetaData);
   const row = serializeRowHeader('M', id) + json + '\n';
   return stringToChunk(row);
 }
diff --git a/packages/react-test-renderer/src/ReactTestRenderer.js b/packages/react-test-renderer/src/ReactTestRenderer.js
index 76911d701de79..43cfe6ef82c8b 100644
--- a/packages/react-test-renderer/src/ReactTestRenderer.js
+++ b/packages/react-test-renderer/src/ReactTestRenderer.js
@@ -65,7 +65,7 @@ type ReactTestRendererJSON = {|
   type: string,
   props: {[propName: string]: any, ...},
   children: null | Array<ReactTestRendererNode>,
-  $$typeof?: Symbol, // Optional because we add it with defineProperty().
+  $$typeof?: symbol, // Optional because we add it with defineProperty().
 |};
 type ReactTestRendererNode = ReactTestRendererJSON | string;
 
diff --git a/packages/react/src/ReactChildren.js b/packages/react/src/ReactChildren.js
index d0562f53e3bc9..686d39a5716a9 100644
--- a/packages/react/src/ReactChildren.js
+++ b/packages/react/src/ReactChildren.js
@@ -137,9 +137,12 @@ function mapIntoArray(
           escapedPrefix +
             // $FlowFixMe Flow incorrectly thinks React.Portal doesn't have a key
             (mappedChild.key && (!child || child.key !== mappedChild.key)
-              ? // $FlowFixMe Flow incorrectly thinks existing element's key can be a number
-                // eslint-disable-next-line react-internal/safe-string-coercion
-                escapeUserProvidedKey('' + mappedChild.key) + '/'
+              ? escapeUserProvidedKey(
+                  // eslint-disable-next-line react-internal/safe-string-coercion
+                  '' +
+                    // $FlowFixMe Flow incorrectly thinks existing element's key can be a number
+                    mappedChild.key,
+                ) + '/'
               : '') +
             childKey,
         );
@@ -190,6 +193,7 @@ function mapIntoArray(
       const iterator = iteratorFn.call(iterableChildren);
       let step;
       let ii = 0;
+      // $FlowFixMe `iteratorFn` might return null according to typing.
       while (!(step = iterator.next()).done) {
         child = step.value;
         nextName = nextNamePrefix + getElementKey(child, ii++);
@@ -222,7 +226,7 @@ function mapIntoArray(
   return subtreeCount;
 }
 
-type MapFunc = (child: ?React$Node) => ?ReactNodeList;
+type MapFunc = (child: ?React$Node, index: number) => ?ReactNodeList;
 
 /**
  * Maps children that are typically specified as `props.children`.
diff --git a/packages/react/src/ReactLazy.js b/packages/react/src/ReactLazy.js
index 6bfa6cbdec413..4f786ed25f968 100644
--- a/packages/react/src/ReactLazy.js
+++ b/packages/react/src/ReactLazy.js
@@ -43,7 +43,7 @@ type Payload<T> =
   | RejectedPayload;
 
 export type LazyComponent<T, P> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   _payload: P,
   _init: (payload: P) => T,
 };
diff --git a/packages/shared/CheckStringCoercion.js b/packages/shared/CheckStringCoercion.js
index 305572f8462c7..e8fbf64a99b88 100644
--- a/packages/shared/CheckStringCoercion.js
+++ b/packages/shared/CheckStringCoercion.js
@@ -26,6 +26,7 @@ function typeName(value: mixed): string {
       (hasToStringTag && (value: any)[Symbol.toStringTag]) ||
       (value: any).constructor.name ||
       'Object';
+    // $FlowFixMe
     return type;
   }
 }
diff --git a/packages/shared/ReactServerContextRegistry.js b/packages/shared/ReactServerContextRegistry.js
index ab8421b3c329a..d8f7c7082940e 100644
--- a/packages/shared/ReactServerContextRegistry.js
+++ b/packages/shared/ReactServerContextRegistry.js
@@ -17,6 +17,7 @@ export function getOrCreateServerContext(globalName: string) {
   if (!ContextRegistry[globalName]) {
     ContextRegistry[globalName] = createServerContext(
       globalName,
+      // $FlowFixMe function signature doesn't reflect the symbol value
       REACT_SERVER_CONTEXT_DEFAULT_VALUE_NOT_LOADED,
     );
   }
diff --git a/packages/shared/ReactSymbols.js b/packages/shared/ReactSymbols.js
index 6ff9305fa7b00..50f4fba27d98a 100644
--- a/packages/shared/ReactSymbols.js
+++ b/packages/shared/ReactSymbols.js
@@ -40,7 +40,7 @@ export const REACT_SERVER_CONTEXT_DEFAULT_VALUE_NOT_LOADED = Symbol.for(
 const MAYBE_ITERATOR_SYMBOL = Symbol.iterator;
 const FAUX_ITERATOR_SYMBOL = '@@iterator';
 
-export function getIteratorFn(maybeIterable: ?any): ?() => ?Iterator<*> {
+export function getIteratorFn(maybeIterable: ?any): ?() => ?Iterator<any> {
   if (maybeIterable === null || typeof maybeIterable !== 'object') {
     return null;
   }
diff --git a/packages/shared/ReactTypes.js b/packages/shared/ReactTypes.js
index 6e829a3a9f689..5209c795c239b 100644
--- a/packages/shared/ReactTypes.js
+++ b/packages/shared/ReactTypes.js
@@ -24,7 +24,7 @@ export type ReactNodeList = ReactEmpty | React$Node;
 export type ReactText = string | number;
 
 export type ReactProvider<T> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   type: ReactProviderType<T>,
   key: null | string,
   ref: null,
@@ -37,13 +37,13 @@ export type ReactProvider<T> = {
 };
 
 export type ReactProviderType<T> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   _context: ReactContext<T>,
   ...
 };
 
 export type ReactConsumer<T> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   type: ReactContext<T>,
   key: null | string,
   ref: null,
@@ -55,7 +55,7 @@ export type ReactConsumer<T> = {
 };
 
 export type ReactContext<T> = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   Consumer: ReactContext<T>,
   Provider: ReactProviderType<T>,
   _currentValue: T,
@@ -85,7 +85,7 @@ export type ServerContextJSONValue =
 export type ReactServerContext<T: any> = ReactContext<T>;
 
 export type ReactPortal = {
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
   key: null | string,
   containerInfo: any,
   children: ReactNodeList,
@@ -99,7 +99,7 @@ export type RefObject = {|
 |};
 
 export type ReactScope = {|
-  $$typeof: Symbol | number,
+  $$typeof: symbol | number,
 |};
 
 export type ReactScopeQuery = (
diff --git a/packages/shared/isValidElementType.js b/packages/shared/isValidElementType.js
index 87424982afc11..c0e4cdc769323 100644
--- a/packages/shared/isValidElementType.js
+++ b/packages/shared/isValidElementType.js
@@ -33,7 +33,7 @@ import {
   enableLegacyHidden,
 } from './ReactFeatureFlags';
 
-const REACT_MODULE_REFERENCE: Symbol = Symbol.for('react.module.reference');
+const REACT_MODULE_REFERENCE: symbol = Symbol.for('react.module.reference');
 
 export default function isValidElementType(type: mixed) {
   if (typeof type === 'string' || typeof type === 'function') {
diff --git a/scripts/flow/config/flowconfig b/scripts/flow/config/flowconfig
index 9c10ba265dce2..a61f324d93e52 100644
--- a/scripts/flow/config/flowconfig
+++ b/scripts/flow/config/flowconfig
@@ -50,4 +50,4 @@ esproposal.optional_chaining=enable
 munge_underscores=false
 
 [version]
-^0.97.0
+^0.122.0
diff --git a/yarn.lock b/yarn.lock
index d94de09d4bea0..62529dd2066a5 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -7923,10 +7923,10 @@ flatted@^2.0.0:
   resolved "https://registry.yarnpkg.com/flatted/-/flatted-2.0.2.tgz#4575b21e2bcee7434aa9be662f4b7b5f9c2b5138"
   integrity sha512-r5wGx7YeOwNWNlCA0wQ86zKyDLMQr+/RB8xy74M4hTphfmjlijTSSXGuH8rnvKZnfT9i+75zmd8jcKdMR4O6jA==
 
-flow-bin@0.97:
-  version "0.97.0"
-  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.97.0.tgz#036ffcfc27503367a9d906ec9d843a0aa6f6bb83"
-  integrity sha512-jXjD05gkatLuC4+e28frH1hZoRwr1iASP6oJr61Q64+kR4kmzaS+AdFBhYgoYS5kpoe4UzwDebWK8ETQFNh00w==
+flow-bin@^0.122:
+  version "0.122.0"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.122.0.tgz#c723a2b33b1a70bd10204704ae1dc776d5d89d79"
+  integrity sha512-my8N5jgl/A+UVby9E7NDppHdhLgRbWgKbmFZSx2MSYMRh3d9YGnM2MM+wexpUpl0ftY1IM6ZcUwaAhrypLyvlA==
 
 fluent-syntax@0.13.0:
   version "0.13.0"