Greetings,
After updating Visual Studio, SDKs, and Uno Platform, I created a new .NET 9 project.
When attempting to build the solution for WinAppSDK, I encountered the following error:

net9.0-windows10.0.19041\win-x64\WinRT.SourceGenerator\Generator.WinRTAotSourceGenerator\WinRTGenericInstantiation.g.cs(25,31,25,48): error CS0227: Unsafe code may only appear if compiling with /unsafe

I have tried to add the AllowUnsafeBlocks and it helps for me.
I am not entirely sure if this issue is specifically related to the Uno Platform Template, but I decided to share this information just in case.