Well, the point is I do not trust either. I am on apple now, but my experience with android is that there are apps you cannot uninstall.
On the other hand I have once tried a custom rom, but it was not a great experience. I do think I will need to try this again.
If you have an existing photo library somewhere on a drive, and load it in immich keeping its own folder structure. In the docker compose file you map the external library to the container.