Test transparency with layered windows by using a SwapChainPanel, which was broken since Windows app SDK 1.1.0 (with black/white background in DirectComposition window)
Only tested on Windows 10 (22H2)
From microsoft/microsoft-ui-xaml#1247, does not work fine on Windows 11 atm (unwanted border + shadow)...
[Edit] Thanks to michalleptuch; I updated code for Windows 11 from his comment
