And to complete the tutorial we need instructions how to restore from a backup as there are no ways to do so in the Yunohost webadmin.
It seems it can be done this way from the yunohost command-line:
borg export-tar /path/to/repo::your_backup your_backup_yunohost.tar.gz
according to [Borg & Borg Server] Deduplicated, encrypted and remote backups - #18 by charly
Then, I suppose, it will show up as a normal backup in the Yunohost webadmin, and from there we can restore individual apps. right?
I will have to check if this works with Borgbase