My comment isn't based on the article, it's based on observing what's actually happening, both from the conference sessions and activity in the various open source projects that it's about. The article is based on public info, so you can observe for yourself.
The truth as of now is that WinUI (the UI stack from UWP) is the only one of these frameworks actually getting significant new feature development. The main reason for this is that unlike winforms or WPF, it doesn't have a dependency on .NET, so it can be used by projects like Windows and Office that for the most part never adopted .NET and managed code.
Like if you watch this session from the conference -> https://www.youtube.com/watch?v=hKMzFjGfoy0 , it's billed as a talk on the Windows presentation platform as a whole, but they spend basically all their time talking about WinUI. The new React Native implementation for Windows is also being built on top of WinUI.