x3i

I don't see anyone mentioning sth power efficient yet, so I will throw my two cents in here; I just ordered an Odroid M1S to take over some jobs from my RPi4 (8GB). Has not yet arrived so I cannot praise it yet but might be worth a look!

Update: seems like the persistence section is sufficient; I have

persistence:
  enabled: true
  existingClaim: nextcloud-config-claim

at the end of my values file which references a volume claim (and volume) that I created manually upfront. The importand file is config.php. Back that thing up immediately and three times, print it if you have to. The secret in there is unrecoverable otherwise and needed for any repair actions.
I also use the postgresql sub-chart (by simply enabling postgresql as database) and provide a claim there:

postgresql:
  enabled: true
global:
    postgresql:
      auth:
        username: XX
        password: YY
        database: nextcloud
  image:
    repository: postgres
    tag: "14"
    postgresqlDataDir: /bitnami/pgdata
  primary:
    persistence:
      enabled: true
      existingClaim: nextcloud-db-claim

Hope it helps!

I think it was literally called "config". I will check my setup and provide the mount points I used here later today, if you back these up, it should work. Put some disposable data on it once you finished setup and then upgrade to a newer version to see if everything works. You can specify the image tag to use manually (or you install an older chart version).
I also pinned the postgres version to 14, not sure if I can recommend that but I had issues with DB upgrades in a docker installation, so I tend to be careful there.

True. Have a setup running on Kubernetes with their helm chart but the documentation is (or at least was) insufficient on what is important to back up, so I had to start over once, learning the hard way that the config file contains the one string you always need for recovering data. Since then, it is pretty stable and I had almost no problems.