Well, yes, but…
nextcloud forked owncloud back when there was only the php codebase.
opencloud forked owncloud ocis, which is a rewrite in go.
So while both forked “owncloud”, or “something named owncloud”, i doubt they’ll have any code in common.
Owncloud seems to be pretty much over IIRC.
The company behind it got bought be some american company in 2023, that promised that everything will “stay as open as it is” - you won’t believe what happened next ;)
Then recently many of the developers left to join OpenCloud, which seems to be a fork of owncloud, lead by a german open source veteran.
I can’t really tell you what to use, but from my personal experience - stay away from glusterfs and drbd. both have caused me serious trouble when trying to run them in a production setup. ceph seems to be pretty solid, though.
I’d stay on zfs, I simply don’t trust btrfs’ raid implementation. For very important documents I also set copies=2 (or 3) on that dataset, just in case.
And as others already said: 3-2-1 backups ;)