I realize this is a very broad question, so to help I'll mention that my primary experience with any programming language is Python. I've looked into C and C++ as well, but I haven't written much in them; in part because they're more involved, and in part because I get lost in the IDE weeds with'em (whether choosing an IDE or getting it configured to even get started tbh, but that's mostly a different topic).
In Python I know there's an option in Tkinter, and I've worked with it to some extent but never got entirely comfortable with it. Maybe it would be best to try making some more stuff with it instead of bouncing around different things, but would that be advisable over something that may be better suited to the task?
If it would be better to stick with it, what might be some things you wish you'd known starting out with GUI programming (whether particular to Python or generally applicable)?
Tbh it's not really what I was going for for learning GUI stuff, it's just the language I'm more familiar with. It sounds like you have something that may be better in mind, in which case what might that be? Also to clarify, I'm more interested in desktop-based GUI programming/development.