Over the past month I've had to write a bunch of GUI apps in tkinter and it was a lot of fun. Everything clicked, and I never felt like I was fighting the toolkit. Now I'd like to learn the finer points of the toolkit. Which rules do each layout (pack, place, grid) use, how events are propagated throughout widget tree, how bind tags actually work, and the difference between fill vs expand. Not a single tkinter book that I've seen covers the more advanced topics. I've found stack overflow to be a better resource, but not very holistic. I'm looking for a book that will reduce the amount of experimentation I'm going to have to do.
Contrast with gtk in C and Python which I used to do many years ago. I never found it fun like tkinter but the docs were pretty good. Great high level conceptual overview, not so great on widget details, and very little on design practices. Contrast with tkinter in which there are millions of ways for encapsulating widgets into classes.
As for QT, I've bounced off that every time I've tried to pick it up.
My point is, I really like tkinter and want to commit to it, with some help.
I would recommend learning Tk and the details of how tkinter wraps Tk https://en.wikipedia.org/wiki/Tk_(software)
These resources might help:
https://www.tcl.tk/
https://tkdocs.com/
https://tkdocs.com/book.html