Does the backup app work properly now? I tested it ~ 6 month ago and nothing worked.
What backup app?
I think you must test it on your own.
More important than a backup, however, is to restore the backup from time to time on a test system. This applies to both the app you cited and the instructions I provided.
Maybe you want to try the Backup/Restore-scripts from @DecaTec at DecaTec/Nextcloud-Backup-Restore: Bash scripts for backup/restore of Nextcloud - Nextcloud-Backup-Restore - Codeberg.org?
I used the scripts to completely backup an instance and restore it on a new VPS once - maybe this is the backup solution you may be searching for?
Does the Decatec solutions work to safe backups on FTP or something else?
any infos about that?