"simple cross-platform GUI+programming language" livecode.com fits that description. It's been my daily driver for years, but full disclosure I'm now looking for something similar to your requirements, but python-based.

Depending on how elaborate your GUI needs are, CardStock might be suitable: https://cardstock.run

Any progress from the openXtalk people trying to keep the opensource of Livecode (from before the rugpull) going?

I bought a book on using QT6 from Python --- hoping to finish an initial read and then give it a try (unless something better comes along).