Readme after installation of Microsoft.UI.Xaml NuGet tells to put <XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" />
into app resources.
But looks like this class does not exist in Uno.
Here I see that it is added in code and with conditional compilation.
This class is not yet supported in Uno at this point. To add support for it on Windows only, you can add the following in your App.xaml.cs
:
#if NETFX_CORE
Resources.MergedDictionaries.Add(new Microsoft.UI.Xaml.Controls.XamlControlsResources());
#endif