Thanks for the Docker file.
I have Nextcloud running.
The NginxProxyMangager in the current version 2.7.1 apparently has a BUG at the moment; login is not possible.
However, Nextcloud itself is very very sluggishly responsive, so I'm considering moving my virtual machines to a NUC and using the Helios64 exclusively with OMV only, which is what I bought it for.
Ps.: I have now disabled Collabora (it was automatically installed during initial setup) and now Nextcloud is much more responsive.