This is what the peer-to-peer app "Nextcloud Backup" can do:

Store backups on another Nextcloud server. The other server can but doesn't have to have the backup app installed
Store backups on external storage, like FTP, SMB, WebDAV or any other Nextcloud-supported protocol. You can also store them on a local drive, like an USB drive attached to your server!
Do manual and / or automatic, scheduled backups in time slots you can configure.
Store the entire Nextcloud installation, including configuration, apps and their data. Note: non-local data, including external storage, is NOT backed-up. Maybe a feature for the future!
Do incremental or full backups in the background (short maintenance mode needed)
Do optional (but recommended and enabled by default) compression and encryption.
Export encryption key and other configuration information to a file or clipboard for safe-keeping.
Give notifications in the Activities app about backup activity.
Exclude folders from backup if you add a .nobackup file in the folder.
Be controlled by the command line to search for and restore single files, initiate full restore, or list and create backups.


Release later this year with Nextcloud 23

mais ça a l'air trop long à installer :
https://docs.nextcloud.com/server/11/admin_manual/installation/source_installation.html

" Il faut simplement lui ajouter un Raspberry Pi  "

(et  http://www.phoronix.com/scan.php?page=news_item&px=OwnCloud-Responds-To-Nextcloud )