I've probably written GUI apps in C, Java, Ruby, Objective-C, Swift, JavaScript, and probably a couple I forgot about. Dart+Flutter come the closest to being "good" and correct. There's some missing documentation for Desktop development with regards to Flutter + Dart but nothing is totally intractable if you're willing to read through issues. My only caveat is that Google is truly an awful company to depend on for your business; since, they 100% do not give a a single fuck about you unless you're paying them ~$100 million or more a year, or an EXTREMELY high profile client.
I've been getting ready to give Pascal a solid try but I still totally lose my mind when working in Lazarus (like where did the thing I just used go? Ah yes, tiny, free-floating window, of course). I have a feeling Pascal is probably the real diamond in the rough of UI application development these days.
Qt is probably fine but their licensing turns me off from ever using or considering it.