GTK4 changed a lot though, like they do not even try anymore, deprecated font dialog because that is better done with XDG portals, but such thing does not even exist. How will that work on macOS and Windows, it cannot? Or what they did with the menus. Toolkits should be user oriented and should not have vision, it just needs to work and provide controls, events, etc., you cannot even position windows in macOS and Windows with GTK4, that is not toolkit that works for users.
I am working on the IUP fork here https://github.com/gen2brain/iup-go , one toolkit to handle them all, and I did my best for GTK4 backend, but from 14 drivers/backends I worked on, it was the worst experience and I had to fight battles with it.
Manifestly yes. There's even a list of GTK4/Adwaita apps available here: https://arewelibadwaitayet.com/