NativeAccessibilityManager.setAccessibilityContentSizeMultipliers(…) not actually changing defaults

Description

On new architecture, NativeAccessibilityManager.setAccessibilityContentSizeMultipliers(…) seems to not actually update the rendered text scales on iOS over the default values hardcoded in https://github.com/facebook/react-native/blob/main/packages/react-native/React/Base/RCTUtils.mm#L366-L377. On old architecture, these reflect immediately.

Reproducible with Expo 53 in 0.79.5, 0.80.1 (npx expo install expo@canary --fix), and 0.80.2 (yarn add react-native@0.80.2).

• Calling it on JavaScript initialization (outside/before render) doesn't work either.
• Interestingly, JS and event handlers report the updated values but the actual rendering does not change. I believe that is why this rn-tester AccessibilityManagerTest still passes.
• As would be expected, patching the values in RCTUtils.mm before building react-native does reflect so these are the ones being used by Fabric.

Aside: I'm not sure what the plan is forNativeAccessibilityManager given the move away from exposing private APIs but the community probably does need a way to update these values.

Steps to reproduce

1. Open https://snack.expo.dev/@shollington-popeyes/fc57d4 (just App.js modified).
2. Make sure you are in non-large Font Scaling mode (iOS settings or button at the bottom of Snack).
3. Click the "Change Accessibility Multipliers" button and observe no actual change in font scaling.

React Native Version

0.80.2

Affected Platforms

Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx @react-native-community/cli info

info Fetching system and libraries information...
System:
  OS: macOS 15.5
  CPU: (10) arm64 Apple M4
  Memory: 143.27 MB / 24.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.17.0
    path: ~/.nvm/versions/node/v22.17.0/bin/node
  Yarn:
    version: 1.22.22
    path: ~/.nvm/versions/node/v22.17.0/bin/yarn
  npm:
    version: 10.9.2
    path: ~/.nvm/versions/node/v22.17.0/bin/npm
  Watchman:
    version: 2025.06.30.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.5
      - iOS 18.5
      - macOS 15.5
      - tvOS 18.5
      - visionOS 2.5
      - watchOS 11.5
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.1 AI-251.25410.109.2511.13665796
  Xcode:
    version: 16.4/16F6
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.15
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native:
    installed: 0.80.2
    wanted: 0.80.2
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

There is no crash. It is visual/rendering/layout issue.

MANDATORY Reproducer

https://snack.expo.dev/@shollington-popeyes/fc57d4

Screenshots and Videos

Old Architecture	New Architecture

packages/react-native/React/Base/RCTUtils.mm にあるハードコードされたデフォルト値から始め、iOS で NativeAccessibilityManager がどのように Fabric に到達するかを追跡します。その経路を rn-tester/IntegrationTests/AccessibilityManagerTest.js と比較し、リンクされた Snack を使って再現します。新しいアーキテクチャでランタイムの倍率の変更がレンダリングされたテキストに反映され、回帰に対するカバレッジがあることが完了の条件です。