I think few people are using the Win32 APIs directly and Microsoft has been shifting their stuff a bunch.
WPF (Windows Presentation Foundation ) had been the recommendation a while back, but then Microsoft started pushing UWP (Universal Windows Platform). Both of those have been succeeded by WinUI 3. UWP has been deprecated. WPF is alive, but more in a maintenance mode while WinUI 3 takes over the future. Oh, and WinForms were popular, but now not.
There's definitely been a lot of shifting and I think that's caused a lot of annoyance in the developer community - especially as Microsoft ships JS/WebView2 based apps instead of dogfooding their own stuff. If you hang out in the dotnet subreddit enough, you'll definitely see Windows devs annoyed at Microsoft's mercurial attitude toward their desktop frameworks and seeming lack of direction/interest - as their big new things are JS/WebView2.
They are talking about UI. Winforms (abandoned), WPF (abandoned), UWP (abandoned), MAUI.
Windows itself was always using their own custom stuff and not any of those. The closest thing to an established framework in Windows is react native that is sprinkled here and there. And QT that OneDrive uses
What are you talking about? The Windows APIs have been stable for at least 20 years.