It should work that way. If you use the recommended Docker Compose scripts for immich, you’ll notice that only a few volumes are mounted to store your data. These volumes don’t include information about running instances. If you take snapshots of these volumes, back them up, remove the containers and volumes, then restore the data and rerun the Compose scripts, you should be right where you left off, without any remnants from previous processes. That’s a pro of container process isolation
This is 100% the best advise. But how do you remember your password managers password? I highly recommend Computerphiles tips, I’ve never seen it explained better: https://youtube.com/watch?v=3NjQ9b3pgIg
(Join 3-4 random, unrelated words for a strong, memorable password)