One cross platform Python framework I found interesting is flet https://flet.dev/ It's powered by Flutter behind the scenes and familiar enough so that you can translate most things from Flutter/Dart tutorials to Flet. I haven't used it and I'll most likely never will (Flutter developer trying to pivot to real native development), but it seems to have an active community, and in theory, it enables developers to write…
Last time I looked at Flet, it gave the impression that you had to use the wrapped Flutter widgets, making it hard to use widgets and packages from pub.dev in a Flet application.
As I see, you can use pure python packages, but not Flutter packages or Python packages with some other languages in the mix.