I made a post about how I upgraded from non-docker v11 to docker v12. You will want to setup a test setup without data first to test with, and then do the setup again but with your data. Also make sure you have an undo plan (backups, snapshot the VM, zfs snapshot, whatever).
I dislike docker, so the instructions talk about using podman instead. I think you can just skip the podman parts, and look at how I moved the data to make an upgrade work for me.
Since writing this, I have moved the database into a podman container too (not because I like it, but it fixed a bug where sometimes seafile would start before the database was ready). I also stopped bypassing the nginx built into the docker image. I don’t like it, but it should make future updates easier.