@tomasv @alex Yes, I know.
I'm not sure if many people in the self-hosting sector are truly aware of some complexity when dealing with PostgreSQL DBs.

My main intention was the advice, that it is not possible to mount the dabase files from a previous PostgreSQL major version without a migration with a new PostgreSQL major version.

Also using pg_upgrade is, when running PostgreSQL in a container, not so easy.
One possible way can be to use this container image:
https://github.com/tianon/docker-postgres-upgrade