I created a new net5.0 WPF application in Visual Studio (16.9.6) and installed the Progress UI for WPF Extension. I added the Telerik Nuget source and installed the package "Telerik.UI.for.Wpf.NetCore.Xaml". I added the Telerik namespace (http://schemas.telerik.com/2008/xaml/presentation) to my main view and I am able to add controls from that namespace in the XAML code just fine including Intellisense support. I also see all the Telerik controls in the VS Toolbox and I can drag controls onto my view in the designer.
But, all the controls are invisible in the designer and also at runtime. No errors during design time or compilation whatsoever. Seems like there is no default theme applied at all. I already tried to explicitly set a theme but all the controls stay invisible. Default WPF controls work without any issue...
I've been working with Telerik and WPF for 10 years now and I never had a similar issue so far. Docs and forums did not lead me on the right trace unfortunately. Help would be much appreciated!