Does breaking stuff happen often? I plan to use the docker image nextcloud:stable-fpm in the hopes of bypassing some bugged releases.

In a span of a year, I had small visual bugs appear, drag and drop not working (have to manually click “upload from computer”). Easiest way to avoid them is to wait before switching to a new major release. So things regularly break, but they’re not essential and your data should always stay safe.

I don’t know the docker container you linked but if it does that, or if you wait a bit before updating, then you should mostly be fine