Ubuntu Touch is still a thing.

We also have PostmarketOS (alpine base) and Mobian (debian base) as frontrunners. Supposedly Arch Linux for ARM and openSUSE Tumbleweed are also used by some on mobile.

There's HarmonyOS [1], which is developed by Huawei, and which has a similar mix of open (OpenHarmony) and proprietary components. I haven't used it, but it's supported by quite a few phones and sort of surprised it wasn't mentioned anywhere on this thread.

[1]: https://en.wikipedia.org/wiki/HarmonyOS