fluent theme issue in .net10.0-windows

[ahdung]

Description

No matter how ThemeMode is Light or Dark, the window always black, not dark, and control behavior not correct, like the TextBox not show clear icon after typed in. at the same time .net9.0-windows is fine.

project here:
WpfApp2.zip

Reproduction Steps

open above project and build it, you will get two exe to show this issue.

Expected behavior

fluent style correct in .net10

Actual behavior

fluent style incorrect in .net10

Regression?

.net9.0 is good.

Known Workarounds

No response

Impact

No response

Configuration

VS2026 18.0.1
Windows 10 x64 19045.3803

Other information

No response

[luojunyuan]

You know what, in WinUI 3, whether it's .NET 9 or .NET 10, the window background in Dark mode is completely black.

[lone7254]

Having the same issue.

[alraseensaad]

Also, that when a textbox is inside the DataGrid in Win 11

[ahdung]

You know what, in WinUI 3, whether it's .NET 9 or .NET 10, the window background in Dark mode is completely black.

@luojunyuan maybe, but I'm talking wpf.

[ahdung]

@alraseensaad these guys didn't do even the slightest bit of testing, even on the LTS version.