On the other hand GTK has been rewritten 3 times and each new version deprecates a bunch of stuff, making it an absolute nightmare for apps to migrate.

Why can’t they stick an app to a specific gtk version? They were fine with what they started it in, what is the reason to migrate?

If the answer is ver++ anxiety, the problem is self-imposed (still better than using winapi).

Needing new features like wayland support? Better DE integration? Distros removing old versions? What an odd question.

What exactly does “wayland support” do to an existing x11 app? How they managed to ship either the app or the wayland without mutual “support” before?

What’s DE integration apart from tray and notifications? Why does an app need any DE integration beyond a tray icon?

These questions are valid, not odd.

Distros removing versions is a distro’s problem. Most gtk versions are installable on popular distros, afaiu.

Anyway, I find most of these points are moot, because they mirror winapi. Gdi -> directx, fonts scaling, need for msvcrts and so on. Looks like an argument for the sake of argument. You can’t make a modern app with winapi either, it will be a blurry non-integrated win2k window like device manager or advanced properties. The difference is you can’t migrate them at all, even MS can not.

All untrue from my perspective so I'm not sure which parallel universes we live in.