Please, delete this subject. I posted on GitHub Nextcloud my problem, it will be more adapted
Replication of whole NC setups isn’t that easy. For large setups with replicated storage backends etc. this is an option but on a raspberry? Would be an interesting project but I know nothing to rely on.
One thing you can do, push backups to your friends server each night. You can use rsync-based solutions, some only transfer the differences compared to the last backup (e.g. rsnapshot). You can put a full data backup and create a current database-dump each night. If you raspberry and data crashes/burns or got stolen, you must get the backup from your friend and setup a new raspberry.