I host my own Lemmy instance and have a user account on it that I use everywhere (I don’t host local communities, I just use it as a home for my Lemmy user account). I needed to re-home my Lemmy server, and though it’s a docker installation, copying the /var/lib/docker/volumes/lemmy_* directories to the new installation didn’t work. So I created a new Lemmy server.
How can I move my old account to the new server, so I can keep all my subscriptions and post/comment history?
The correct way (for your use case) is probably to do a full backup of the database and pictrs database and then import them into the new instance.
This is covered in the documentation