I have a feeling that most python GUIs are lacking in some area and for full creative freedom someone would have to go for flask or fastapi, build the UI with modern js-frontend frameworks and connect that frontend with the actual application using websockets or regular HTTP-Requests.
Without it I couldn't have produced Captain's Log, for example : https://captainslog.scarygliders.net/captains-log-2/
The initial version, 5 or so years ago (maybe a bit more, I do not remember) was based on a python library (sorry, I forgot the name but it was the major one at the time). It worked fine for a bit but moving to a kiosk browser and vue.js completely changed the game.
The backend was Python, then got replaced by a bus (mqtt) updated via golang microservices (they were in python initially, but then I wanted to learn go)