I tried to use Mono several times, starting from Ximian and Xamarin times, and I always encountered strange problems that were not present in the original applications. I hope they improved somewhat recently because the code produced back then was often unusable (e.g. huge leaks after a couple of hours of use.)
the native grumpy old people like me will continue to use Windows forms or WPF or MFC,ATL,Win32.
The masochists will try to use the open-source silverlight replacement. Moonlight?
The futurists will use Avalonia. Maybe SAFE stack MVU via Fable?
The Microsoft contractors will use WinUI3.
Vast majority of web developers today will use electron, as unfortunate as that is...
Your Silverlight replacement would be OpenSilver.
The cross platform toolkits would be MAUI (nee Xamarin) and Blazor.
Electron is the new Active Desktop/XUL, its fashion phase will eventually fade away.
Can you share the official source of this statement?