For what it’s worth, I tried making a GTK4 app. I got started, created a window, created a header bar, then went to add a url/path entry widget and everything fell apart.
Entry suggestions/completions are formally deprecated with no replacement since 2022. When I did get them working on the deprecated API there was an empty completion option that would segfault if clicked. The default behaviour didn’t hide completions on window unfocus, so my completions would hover over any other open window. There was seemingly no way to disambiguate tab vs enter events… it just sucked.
So after adding one widget I abandoned the project. It felt like the early releases of SwiftUI where you could add a list view but then would run into weird issues as soon as you tried adding stuff to it.
Similarly trying to build an app for macOS practically depends on Swift by Sundell Hacking with Swift or others to make up for Apple’s lack of documentation in many areas. For years stuff like NSColor vs Color and similar API boundaries added friction, and the native macOS SwiftUI components just never felt normal while I tried making apps.
As heavy as web libraries and electron are, at least work mostly out of the box.
There are definitely a shortage of good GUI toolkits - making one is a huge undertaking. GTK is mediocre, as you discovered.
QtWidgets is extremely good though, even if it is effectively in maintenance mode.
Avalonia also seems good too though I haven't used it myself.