[WinUI][CollectionView2]GroupHeader Appearance Differs from CV1

[SuthiYuvaraj]

Description

The GroupHeader rendering in the current implementation differs from CV1. The spacing behavior has changed, resulting in a different visual alignment.

Steps to Reproduce

1. Run the attached sample
2. Ensure the CollectionView is configured with grouping enabled
3. Load grouped data with GroupHeader
4. Observe the spacing around the GroupHeader and items

Expected Behavior
The GroupHeader spacing should match the CV1 behaviour, maintaining consistent spacing around the GroupHeader and the items.

Actual Behavior
The GroupHeader is rendered without additional spacing , aligned similar to the grouping

CV1 Behavior	CV2 Behavior

Link to public reproduction project repository

https://github.com/SuthiYuvaraj/Samples/tree/main/CollectionView2WinUI/TestSampleGrouping

Version with bug

11.0.0-preview2

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

Unknown/Other

Affected platforms

Windows

Affected platform versions

No response

Did you find any workaround?

No response

Relevant log output

[Ahamed-Ali]

This issue has been validated in Visual Studio 18.4.1 in BugFixes_WinUI_CV2 branch . It can be reproducible on Windows platform.