I have a similar set up. I have a NextCloud server set up in my house, running as a docker container. A cron job shuts it down in the middle of the night and runs a full, true backup process up to AWS, and restarts it when done. The convenience of file sync techs with the safety of backup.

(The main utility of docker to me in this case is just being able to assert with absolute certainty, "here are all the directories NextCloud is storing data in". There's nowhere for unbacked-up state to be hiding.)

If I were running this at scale, I'd have some things to worry about, but at this scale, it's fine.