SectionList scrollbar not visible without getItemLayout prop

[marodrui]

Problem Description

When using a SectionList component without the getItemLayout prop (i.e., with dynamic/variable height items), the vertical scrollbar does not render at all. The list content is still scrollable via mouse wheel, but no scrollbar indicator is visible.

When getItemLayout is provided (even with an inaccurate estimated fixed height), the scrollbar appears. However, providing getItemLayout with a fixed height is not suitable for all use cases of React Native Windows.

My understanding is that the SectionList should display a scrollbar when content overflows, regardless of whether getItemLayout is provided.

Steps To Reproduce

1. Create a SectionList with multiple sections and enough items to overflow the container, using variable-height items (no getItemLayout prop):

   <SectionList
       sections={sections}
       keyExtractor={(item) => item.id}
       renderItem={({ item }) => <VariableHeightItem item={item} />}
       renderSectionHeader={({ section }) => <SectionHeader title={section.title} />}
   />

2. Run the app

3. Observe that the list content is scrollable (mouse wheel / touch), but no scrollbar is visible.

4. Now add a getItemLayout prop with any fixed height estimate:

   <SectionList
       sections={sections}
       keyExtractor={(item) => item.id}
       renderItem={({ item }) => <VariableHeightItem item={item} />}
       renderSectionHeader={({ section }) => <SectionHeader title={section.title} />}
       getItemLayout={(_, index) => ({
           length: 100,
           offset: 100 * index,
           index,
       })}
   />

5. The scrollbar now appears.

Expected Results

No response

CLI version

20.0.0

Environment

info Fetching system and libraries information...
System:
  OS: Windows 11 10.0.26100
  CPU: (12) x64 13th Gen Intel(R) Core(TM) i7-1365U
  Memory: 5.22 GB / 31.64 GB
Binaries:
  Node:
    version: 22.13.0
    path: C:\nvm4w\nodejs\node.exe
  Yarn:
    version: 1.22.22
    path: C:\Program Files (x86)\Yarn\bin\yarn.CMD
  npm:
    version: 10.9.2
    path: C:\nvm4w\nodejs\npm.CMD
  Watchman: Not Found
SDKs:
  Android SDK: Not Found
  Windows SDK:
    AllowDevelopmentWithoutDevLicense: Enabled
    AllowAllTrustedApps: Enabled
    Versions:
      - 10.0.19041.0
      - 10.0.22621.0
      - 10.0.26100.0
IDEs:
  Android Studio: Not Found
  Visual Studio:
    - 16.11.36602.28 (Visual Studio Professional 2019)
    - 17.14.36623.8 (Visual Studio Community 2022)
Languages:
  Ruby:
    version: 3.0.2
    path: C:\tools\ruby30\bin\ruby.exe
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.0
    wanted: 20.0.0
  react:
    installed: 19.1.4
    wanted: 19.1.4
  react-native:
    installed: 0.81.6
    wanted: 0.81.6
  react-native-windows:
    installed: 0.81.12
    wanted: 0.81.12
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Community Modules

No response

Target React Native Architecture

None

Target Platform Version

None

Visual Studio Version

None

Build Configuration

None

Snack, code example, screenshot, or link to a repository

No response

[vineethkuttan]

I have tried reproducing this issue in RNW 0.81.13 , but I could not reproduce it. I have attached my jsx here for reference.
Please have a look and let me know if I am missing something.

SectionList.mp4

App.tsx.txt