Wouldn’t unlocking the bootloader and installing a custom ROM be easier, more stable and cheaper than buying a niche product that’s unlikely to work properly?

What exactly are you looking for? Android IS Linux, do you want to try a different “distribution” just for fun?

Made my own for myself and some friends. We couldn’t be bothered creating account on the larger instances and have power tripping admins de-federating instances over trivial issues.

I think bitwarden fills all of your requirements.