exactly, when for example the nextcloud documentation says:
To start the container type: docker run -d -p 8080:80 nextcloud
is not exactly clear that all the data will be 100% lost when the docker container is closed
And when it says more down in the docs “just use volumes to persist data” - yeah how to backup those volumes? No mention at all…
Should tell to mount a directory rather than a volume. Backup a directory is easy and everyone can do it, backup a docker volume, good luck, your data has an invisible time bomb