What WPF mess are you talking about? Aside from Visual Studio, I can't think of many first-party GUIs that are written in WPF.
Admittedly I know WPF needs good graphics hardware which I'm sure Citrix is not providing.
I know we need to scale for different screens but the reality is it's slower then ever on faster hardware.
UWP/WinUI/Metro uses XAML and Microsoft was very committed to that for a while. UWP didn't really pan out, but that was for reasons other than XAML and WinUI IMO.