Well new GTK is claiming that they're making it easier to write non-gnome GTK apps. What that looks like to me is that a lot of functionality is moving into a g

Well new GTK is claiming that they're making it easier to write non-gnome GTK apps. What that looks like to me is that a lot of functionality is moving into a gnome-specific library (libadwaita) and you'll need to find another provider for those gnome specific widgets and functions and stuff. Pop OS makes another add-on library like that. Meanwhile QT continues to work great and they've largely solved the licensing issues that were a problem in the past. It's also a comparatively stable project and supports targets like android, iOS, rendering directly on to buffers (you can embed it into games). If you're starting a new project I think QT should be your default unless you have a good reason to use GTK. I'm not qualified to assess the code quality of either project, but I have been impressed by QT for the few things I've needed to build a gui for. Things just work but if you need really specific functionality (like rendering directly to a framebuffer with no display server on embedded linux) it's not too hard to make it work. I'm honestly a bit mystified as to why anyone would choose GTK for a new project, unless they were specifically targeting the Gnome desktop and only the Gnome desktop.