Strangely VS did not give me an error upon building the app.
First of all, please check the official document about the XAML errors and warnings to check if you have enabled it or not.
And then, I have tested the similar code in the Visual Studio 2022 17.10.2 and Visual Studio 17.11.0 Preview 2.0.
In Visual Studio 17.11.0 Preview 2.0: It will show the XFC0066 Invalid Xaml error when I built or run the project.
In the Visual Studio 2022 17.10.2: It will show the the Error XFC0000 Cannot resolve type error when I built and run the project.