RibbonWindow not working correctly with ThemeMode="System"

### Description

RibbonWindow fails to correctly render if **ThemeMode="System"** is in either App.xaml or MainWindow.xaml. RibbonWindow and Ribbon are well written but seem to have missed the modernization in dotnet 9.

### Reproduction Steps

Any valid RibbonWindow fails to render the quick access toolbar in the window title bar in a net9.0-windows or net10.0-windows project if any ThemeMode is set. I'm currently testing with 10.0.100-preview.2.25164.34.

### Expected behavior

Quick access toolbar in the window title bar.

### Actual behavior

See image in expected behavior.

### Regression?

_No response_

### Known Workarounds

_No response_

### Impact

_No response_

### Configuration

_No response_

### Other information

_No response_