Comment by realusername

PostmarketOS doesn't use the Android codebase, they work on upstreaming devices with a standard Linux kernel, so the opposite. They act mostly the same way as a desktop distribution. They do use the downstream image but mostly as a reference to remove it.

Ubuntu Touch does use the Android vendor images though through the libhybris compatibility layer, that's why they have some good compatibility, if the phone has a lineageos image, there's a good chance that it'll work with Ubuntu Touch.

The downside of that is the same as Lineageos, they are stuck on whatever kernel the device shipped with and it can be ancient.