diff --git a/projects/js-packages/ai-client/changelog/fix-misc-react-19-stuff b/projects/js-packages/ai-client/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..295742aecbf1
--- /dev/null
+++ b/projects/js-packages/ai-client/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: fixed
+Comment: Fix typing for React 19: onInput is an `InputEvent`, not a `ChangeEvent`.
+
+
diff --git a/projects/js-packages/ai-client/src/logo-generator/components/prompt.tsx b/projects/js-packages/ai-client/src/logo-generator/components/prompt.tsx
index 7774c23b2f30..1541d3ae9fbc 100644
--- a/projects/js-packages/ai-client/src/logo-generator/components/prompt.tsx
+++ b/projects/js-packages/ai-client/src/logo-generator/components/prompt.tsx
@@ -30,7 +30,7 @@ import './prompt.scss';
  * Types
  */
 import type { ImageStyle, ImageStyleObject } from '../../hooks/use-image-generator/constants.ts';
-import type { ChangeEvent, ClipboardEvent, KeyboardEvent } from 'react';
+import type { ClipboardEvent, InputEvent, KeyboardEvent } from 'react';
 
 const debug = debugFactory( 'jetpack-ai-calypso:prompt-box' );
 
@@ -57,8 +57,8 @@ export const AiModalPromptInput = ( {
 } ) => {
 	const inputRef = useRef< HTMLDivElement | null >( null );
 
-	const onPromptInput = ( event: ChangeEvent< HTMLInputElement > ) => {
-		setPrompt( event.target.textContent || '' );
+	const onPromptInput = ( event: InputEvent< HTMLInputElement > ) => {
+		setPrompt( ( event.target as HTMLInputElement ).textContent || '' );
 	};
 
 	const onPromptPaste = ( event: ClipboardEvent< HTMLInputElement > ) => {
diff --git a/projects/js-packages/charts/changelog/fix-misc-react-19-stuff b/projects/js-packages/charts/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..975a4a94cf95
--- /dev/null
+++ b/projects/js-packages/charts/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: changed
+Comment: Fix typing for React 19: `FC<>` now wants to allow for returning async, which the places we use `renderLabel` and `renderLabelPopover` can't actually handle. So declare their types without the `FC<>` helper.
+
+
diff --git a/projects/js-packages/charts/changelog/fix-misc-react-19-stuff#2 b/projects/js-packages/charts/changelog/fix-misc-react-19-stuff#2
new file mode 100644
index 000000000000..d257ee09cc23
--- /dev/null
+++ b/projects/js-packages/charts/changelog/fix-misc-react-19-stuff#2
@@ -0,0 +1,5 @@
+Significance: patch
+Type: changed
+Comment: React 19 recognizes `popoverTarget` and `popoverTargetAction`, and rejects `popovertarget` and `popovertargetaction`, while React 18 needs the latter as it doesn't recognize the former. So supply whichever is appropriate at runtime based on the React version.
+
+
diff --git a/projects/js-packages/charts/src/charts/line-chart/private/line-chart-annotation-label-popover.tsx b/projects/js-packages/charts/src/charts/line-chart/private/line-chart-annotation-label-popover.tsx
index c3bf2692f4bb..1a5a81e1b579 100644
--- a/projects/js-packages/charts/src/charts/line-chart/private/line-chart-annotation-label-popover.tsx
+++ b/projects/js-packages/charts/src/charts/line-chart/private/line-chart-annotation-label-popover.tsx
@@ -1,14 +1,17 @@
 import { __ } from '@wordpress/i18n';
 import { Stack } from '@wordpress/ui';
 import clsx from 'clsx';
-import { useEffect, useId, useRef, useState } from 'react';
+import { useEffect, useId, useRef, useState, version as reactVersion } from 'react';
 import { isSafari } from '../../../utils';
 import styles from '../line-chart.module.scss';
 import type { ButtonWithPopover, PopoverElement, ToggleEvent } from '../../../types';
-import type { FC } from 'react';
+import type { FC, ReactNode } from 'react';
 
 export const POPOVER_BUTTON_SIZE = 44;
 
+// @todo Remove this (and uses of it below) when we drop support for WordPress versions shipping React 18.
+const isReact18 = reactVersion.startsWith( '18.' );
+
 const CloseIcon = () => (
 	<svg
 		width="16"
@@ -29,8 +32,8 @@ const CloseIcon = () => (
 interface LineChartAnnotationLabelWithPopoverProps {
 	title: string;
 	subtitle?: string;
-	renderLabel: FC< { title: string; subtitle?: string } >;
-	renderLabelPopover: FC< { title: string; subtitle?: string } >;
+	renderLabel: ( props: { title: string; subtitle?: string } ) => ReactNode;
+	renderLabelPopover: ( props: { title: string; subtitle?: string } ) => ReactNode;
 }
 
 const LineChartAnnotationLabelWithPopover: FC< LineChartAnnotationLabelWithPopoverProps > = ( {
@@ -83,7 +86,9 @@ const LineChartAnnotationLabelWithPopover: FC< LineChartAnnotationLabelWithPopov
 		<div className={ styles[ 'line-chart__annotation-label' ] }>
 			<button
 				ref={ buttonRef }
-				{ ...( { popovertarget: popoverId } as ButtonWithPopover ) }
+				{ ...( isReact18
+					? ( { popovertarget: popoverId } as ButtonWithPopover )
+					: { popoverTarget: popoverId } ) }
 				className={ styles[ 'line-chart__annotation-label-trigger-button' ] }
 				style={ {
 					width: `${ POPOVER_BUTTON_SIZE }px`,
@@ -110,10 +115,15 @@ const LineChartAnnotationLabelWithPopover: FC< LineChartAnnotationLabelWithPopov
 						{ renderLabelPopover( { title, subtitle } ) }
 					</div>
 					<button
-						{ ...( {
-							popovertarget: popoverId,
-							popovertargetaction: 'hide',
-						} as ButtonWithPopover ) }
+						{ ...( isReact18
+							? ( {
+									popovertarget: popoverId,
+									popovertargetaction: 'hide',
+								} as ButtonWithPopover )
+							: {
+									popoverTarget: popoverId,
+									popoverTargetAction: 'hide',
+								} ) }
 						className={ styles[ 'line-chart__annotation-label-popover-close-button' ] }
 						aria-label={ __( 'Close', 'jetpack-charts' ) }
 					>
diff --git a/projects/js-packages/charts/src/charts/line-chart/stories/index.api.mdx b/projects/js-packages/charts/src/charts/line-chart/stories/index.api.mdx
index a21073f03eae..598c331584ff 100644
--- a/projects/js-packages/charts/src/charts/line-chart/stories/index.api.mdx
+++ b/projects/js-packages/charts/src/charts/line-chart/stories/index.api.mdx
@@ -64,8 +64,8 @@ Individual annotation component for highlighting specific data points or events.
 | `subtitle` | `string` | - | Additional descriptive text |
 | `subjectType` | `'circle' \| 'line-vertical' \| 'line-horizontal'` | `'circle'` | Visual annotation style |
 | `styles` | `AnnotationStyles` | - | Custom styling options |
-| `renderLabel` | `FC<{title: string, subtitle?: string}>` | - | Custom label component. **Disables smart positioning.** |
-| `renderLabelPopover` | `FC<{title: string, subtitle?: string}>` | - | Interactive popover content |
+| `renderLabel` | `(props: {title: string, subtitle?: string} ) => ReactNode` | - | Custom label component. **Disables smart positioning.** |
+| `renderLabelPopover` | `(props: {title: string, subtitle?: string}) => ReactNode` | - | Interactive popover content |
 | `testId` | `string` | - | Test identifier |
 
 ## SeriesData Type
diff --git a/projects/js-packages/charts/src/charts/line-chart/types.ts b/projects/js-packages/charts/src/charts/line-chart/types.ts
index 823d50af662b..c191ff6fb001 100644
--- a/projects/js-packages/charts/src/charts/line-chart/types.ts
+++ b/projects/js-packages/charts/src/charts/line-chart/types.ts
@@ -10,7 +10,7 @@ import type {
 } from '../../types';
 import type { CrosshairStyle, RenderTooltipParams } from '../../visx/types';
 import type { GlyphProps } from '@visx/xychart';
-import type { ReactNode, SVGProps, FC, CSSProperties } from 'react';
+import type { ReactNode, SVGProps, CSSProperties } from 'react';
 
 export type LineChartAnnotationProps = {
 	datum: DataPointDate;
@@ -19,8 +19,8 @@ export type LineChartAnnotationProps = {
 	subjectType?: 'circle' | 'line-vertical' | 'line-horizontal';
 	styles?: AnnotationStyles;
 	testId?: string;
-	renderLabel?: FC< { title: string; subtitle?: string } >;
-	renderLabelPopover?: FC< { title: string; subtitle?: string } >;
+	renderLabel?: ( props: { title: string; subtitle?: string } ) => ReactNode;
+	renderLabelPopover?: ( props: { title: string; subtitle?: string } ) => ReactNode;
 };
 
 export type CurveType = 'smooth' | 'linear' | 'monotone';
diff --git a/projects/js-packages/components/changelog/fix-misc-react-19-stuff b/projects/js-packages/components/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..bb1558af6070
--- /dev/null
+++ b/projects/js-packages/components/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: removed
+Comment: React 19 wants `transformOrigin`, while 18 needs `transform-origin`. It turns out there are no transforms anymore needing an origin in the first place, so just remove it.
+
+
diff --git a/projects/js-packages/components/components/donut-meter/index.tsx b/projects/js-packages/components/components/donut-meter/index.tsx
index 279a73d2dd27..afc42746d7bd 100644
--- a/projects/js-packages/components/components/donut-meter/index.tsx
+++ b/projects/js-packages/components/components/donut-meter/index.tsx
@@ -134,7 +134,6 @@ const DonutMeter: FC< DonutMeterProps > = ( {
 					cy="20"
 					r="15.91549430918954"
 					fill="transparent"
-					transform-origin="center" // eslint-disable-line react/no-unknown-property -- @todo Switch to transformOrigin when we use React 19.
 					strokeWidth={ thickness }
 					strokeDasharray={ `${ percentage } ${ 100 - percentage }` }
 					strokeDashoffset="-25" // this ensures the segment begins at the bottom of the donut instead of the top
diff --git a/projects/packages/backup/changelog/fix-misc-react-19-stuff b/projects/packages/backup/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..c3658dddf654
--- /dev/null
+++ b/projects/packages/backup/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: fixed
+Comment: The `useRestore` test was advancing jest's fake timer by a large amount. React 19 doesn't like this: it doesn't get a gap between updates and winds up throwing a "Maximum update depth exceeded" error. Advance in steps of `POLL_INTERVAL_MS` instead, which gives React 19 the gaps it needs.
+
+
diff --git a/projects/packages/backup/src/dashboard/hooks/test/use-restore.test.ts b/projects/packages/backup/src/dashboard/hooks/test/use-restore.test.ts
index 56b0335b846d..f0643ca55766 100644
--- a/projects/packages/backup/src/dashboard/hooks/test/use-restore.test.ts
+++ b/projects/packages/backup/src/dashboard/hooks/test/use-restore.test.ts
@@ -7,7 +7,7 @@ import apiFetch from '@wordpress/api-fetch';
 import { createElement, type ReactNode } from 'react';
 import { pickLiveRestore } from '../../data/api/restore';
 import { DEFAULT_RESTORE_ITEMS } from '../../types/restore';
-import { useRestore } from '../use-restore';
+import { useRestore, POLL_INTERVAL_MS } from '../use-restore';
 
 jest.mock( '@wordpress/api-fetch', () => ( { __esModule: true, default: jest.fn() } ) );
 const mockedApiFetch = apiFetch as unknown as jest.Mock;
@@ -97,9 +97,13 @@ function submitAll( result: RenderedRestore ) {
  * @param ms - How far to advance.
  */
 async function advance( ms: number ) {
-	await act( async () => {
-		await jest.advanceTimersByTimeAsync( ms );
-	} );
+	// Advance in small steps (POLL_INTERVAL_MS). Longer steps never give React 19 a gap between updates, so it throws "Maximum update depth exceeded".
+	while ( ms > 0 ) {
+		await act( async () => {
+			await jest.advanceTimersByTimeAsync( Math.min( ms, POLL_INTERVAL_MS ) );
+		} );
+		ms -= POLL_INTERVAL_MS;
+	}
 }
 
 /**
diff --git a/projects/packages/backup/src/dashboard/hooks/use-restore.ts b/projects/packages/backup/src/dashboard/hooks/use-restore.ts
index ccd512c7db0d..62e955a2b40b 100644
--- a/projects/packages/backup/src/dashboard/hooks/use-restore.ts
+++ b/projects/packages/backup/src/dashboard/hooks/use-restore.ts
@@ -41,7 +41,7 @@ type Result = {
  * no responsiveness and costs a WordPress.com round trip per tick for its
  * whole duration.
  */
-const POLL_INTERVAL_MS = 5000;
+export const POLL_INTERVAL_MS = 5000;
 
 /**
  * How long the screen will go without a recognisable sign of life before
diff --git a/projects/packages/publicize/_inc/components/manage-connections-modal/tests/index.test.jsx b/projects/packages/publicize/_inc/components/manage-connections-modal/tests/index.test.jsx
index 619c9a7f9491..d31c2aaa2967 100644
--- a/projects/packages/publicize/_inc/components/manage-connections-modal/tests/index.test.jsx
+++ b/projects/packages/publicize/_inc/components/manage-connections-modal/tests/index.test.jsx
@@ -35,10 +35,10 @@ describe( 'ManageConnectionsModal', () => {
 		// some via timers) so no state update escapes act.
 		await act( async () => {
 			await Promise.resolve();
-			jest.runAllTimers();
+			await jest.runAllTimersAsync();
 		} );
 		await act( async () => {
-			jest.runAllTimers();
+			await jest.runAllTimersAsync();
 		} );
 	};
 
diff --git a/projects/packages/publicize/changelog/fix-misc-react-19-stuff b/projects/packages/publicize/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..976b32bf6503
--- /dev/null
+++ b/projects/packages/publicize/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: fixed
+Comment: The `ManageConnectionsModal` test breaks in React 19. Using `await jest.runAllTimersAsync()` instead of `jest.runAllTimers()` in the already-async `act()` call fixes this.
+
+
diff --git a/projects/packages/videopress/changelog/fix-misc-react-19-stuff b/projects/packages/videopress/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..f54ede92f1d5
--- /dev/null
+++ b/projects/packages/videopress/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: fixed
+Comment: Fix another argless `useRef` added since #53002 fixed all the rest. Sigh.
+
+
diff --git a/projects/packages/videopress/routes/video/stage.tsx b/projects/packages/videopress/routes/video/stage.tsx
index 5cf399baf57b..be87a66f772d 100644
--- a/projects/packages/videopress/routes/video/stage.tsx
+++ b/projects/packages/videopress/routes/video/stage.tsx
@@ -511,7 +511,7 @@ const StageInner = () => {
 		? id
 		: Object.keys( completedUploads ).find( key => completedUploads[ key ] === id );
 	const queuedUpload = uploadQueue.find( item => item.id === id );
-	const retainedUpload = useRef< UploadItem >();
+	const retainedUpload = useRef< UploadItem >( undefined );
 	// Keep the editor present if queue cleanup precedes a slow attachment fetch.
 	if ( queuedUpload ) {
 		retainedUpload.current = queuedUpload;
diff --git a/projects/plugins/jetpack/_inc/client/ai/test/main.jsx b/projects/plugins/jetpack/_inc/client/ai/test/main.jsx
index 28d6cb19ef2d..51709e74c9f3 100644
--- a/projects/plugins/jetpack/_inc/client/ai/test/main.jsx
+++ b/projects/plugins/jetpack/_inc/client/ai/test/main.jsx
@@ -371,7 +371,9 @@ describe( 'AI admin page (main.jsx)', () => {
 			);
 			// One page-level notice — AiFeatures must not render a second copy.
 			expect( screen.getAllByText( MASTER_OFF_TITLE, IGNORE_A11Y ) ).toHaveLength( 1 );
-			expect( screen.getByRole( 'checkbox', { name: /Writing Assistant/ } ) ).toBeDisabled();
+			await expect(
+				screen.findByRole( 'checkbox', { name: /Writing Assistant/ } )
+			).resolves.toBeDisabled();
 		} );
 
 		test( 'a host without My Jetpack is sent to the modules page instead', async () => {
diff --git a/projects/plugins/jetpack/changelog/fix-misc-react-19-stuff b/projects/plugins/jetpack/changelog/fix-misc-react-19-stuff
new file mode 100644
index 000000000000..9a0e9407045e
--- /dev/null
+++ b/projects/plugins/jetpack/changelog/fix-misc-react-19-stuff
@@ -0,0 +1,5 @@
+Significance: patch
+Type: other
+Comment: An `AI admin page` test was looking for the "Writing Assistant" checkbox synchronously, even though it gets added asynchronously and all the other tests look for it async. Somehow this worked ok in React 18, but breaks in 19; looking async like everything else does fixes it.
+
+