Google’s Android, the world’s most widely used mobile operating system, started life as open-source software. In its quest for ever-greater profits, the tech giant has been gradually eroding Android’s open-source nature over the last decade.
Originally published on The Lever, but that one asks you to sign up.
Your options are mostly UBTouch and PostmarketOS. Due to how PMOS is designed, it doesnt fully function on the phones it supports. UBTouch does work well due to the ability to use a driver compatibility layer with android IIRC, but you still have the issue of needing a phone that can support it. (I think the latest pixel UBTouch runs on is the 3?)
also, the security model of mobile linux is nowhere near what android is. Things that keep android secure like verified boot are not yet implemented on linux phone OSes AFAIK