There is a galaxy of projects around Kivy, such as https://github.com/kivy/python-for-android to compile python project for Android (with Kivy or not) or https://plyer.readthedocs.io/en/latest/ for cross plateform API (notifications, hardware, filechooser, etc).
For UI there is https://github.com/kivymd/KivyMD for Material design on top of Kivy.
And the team is nice (I've met some of them at PyCon or FOSDEM).
The framework is pleasant to use, and there is a descriptive language, kv, which is really great.
Cross compiling may be painful though (I did it for Android) and the app loading time is a bit long, but it's working.
Some things may be missing in comparison to big frameworks such as Qt, there is no WebView for instance, and accessibility is unfortunately not as good.
It's overall a very good project and it's a pity that it's not more known and used.
I used Kivy once a few years ago for a device that had strict constraints on what it could run with the requirement to run the same code on desktop too (to display the same data). It worked very well for that.
It was not an elaborate app, so I cannot comment on how well it might work with something bigger, but it worked very well for what I needed.
I believe Qt's offering of Qt for Python/PySide6 even uses python-for-android in their android-deploy utility[1].
[1] https://www.qt.io/blog/taking-qt-for-python-to-android
It's pretty new though, and it's a bit rough around the edges still. The other issue is that almost every single package/library for pyside6 only supports QtWidgets, not QML. Meaning you wouldn't be able to use tons of libraries that make up the python qt ecosystem (for example, pyqtwidgets or vispy). Not a huge dealbreaker but it's something to keep in mind.
Yeah, it seems pretty half-baked at the moment. It looks like QML is the intended target for mobile apps on the Qt side.
Yep I don't think there's a practical way to use qtwidgets on mobile, so it's not like Qt is treating pyside differently. It's just that the ecosystem doesn't really follow. I wonder if that's different on the c++ side. Is QML more prevalent in the c++ qt ecosystem?
Thanks for sharing your experience and links! Based on plyer's GH, it looks like you could use it to develop an iOS and Android app. If it supported more APIs (like Health Kit, accessibility), I would try it in a heartbeat.
https://github.com/kivy/plyer