ScrollView as child of Modal no longer scrollable on first mount/modal opening, RN >= 0.76, Android only, old-arch only

Description

Since React Native 0.76.0, a ScrollView as a child of the built-in Modal component is no longer scrollable when the modal first opens on Android.

This seems to only affect the old architecture. New architecture seems to be unaffected.
iOS seems unaffected.

The problem is still present in RN 0.77. Downgrading to 0.75.4 fixes it.

Steps to reproduce

1. Install the reproduction app with yarn android. The reproduction is set to use the old architecture by default.
2. Click the Open Scrollable Modal button.
3. Observe that the screen doesn't scroll, even though it should.
4. Leave the modal open. Try modifying the code in ScrollableModalContent.tsx by adding a style={{flex: 1}} to the ScrollView and saving the file. This hot-reloads the component without unmounting at the parent, and suddenly the ScrollView becomes scrollable.
5. Close the modal using the hardware back button. Re-open the modal, observing the content is unscrollable again, even with style={{flex: 1}} still on the ScrollView.
6. Remove the style={{flex: 1}} from the ScrollView and save the file.
7. Enable newArch in Android gradle.properties.
8. Rebuild the app and try opening the modal again.
9. The modal opens and the content inside scrolls as expected.

React Native Version

0.77.0

Affected Platforms

Runtime - Android

Output of npx react-native info

System:
  OS: Linux 6.12 openSUSE Tumbleweed 20250117
  CPU: (8) x64 Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz
  Memory: 11.91 GB / 31.31 GB
  Shell:
    version: 5.2.37
    path: /bin/bash
Binaries:
  Node:
    version: 20.18.1
    path: ~/.nvm/versions/node/v20.18.1/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/local/bin/yarn
  npm:
    version: 10.8.2
    path: ~/.nvm/versions/node/v20.18.1/bin/npm
  Watchman: Not Found
SDKs:
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.4.1
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.0.1
    wanted: 15.0.1
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.77.0
    wanted: 0.77.0
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: false
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

N/A

Reproducer

https://github.com/goguda/react-native-android-scrollview-in-modal-not-always-scrolling-point-76-up

Screenshots and Videos

No response

首先使用 yarn android 运行链接的复现程序，然后检查 ScrollableModalContent.tsx 和 gradle.properties 中的 Android 设置，同时比较旧架构和新架构的行为。完成标准是：在 Android 旧架构下首次打开 modal 时，ScrollView 可以滚动，同时保持新架构和 iOS 未受影响的行为。