Just a heads up, you'll need to back up the database as well in order to completely mirror Nextcloud.
If you're not worried about the back copy being usable via nextcloud and just want a copy of your files (e.g. to upload them to another Nextcloud instance) rsync will work just fine.
How do I know this? I'm also a Nextcloud admin. 🙂👋
If you want deduplicated, compressed, encrypted, off site backups (yes, you CAN have all of these things!), check out borgmatic (which uses borg backup). Goes over SSH, the backup node never has the ability to decrypt the data, and there are integrity checks so they can't covertly modify contents either. They just have to be trusted with regards to availability.
I'd be happy to answer any questions not covered by the documentation.
