A backup solution for Nextcloud (although you still provide the storage ;) as an actual Nextcloud application.

I don't know why I didn't think of this so far.

Restic still definitely has an edge in encryption/deduplication and advanced feature set but this seems way easier to get going - and moves as one coherent package with your Nextcloud instance (i.e. it backs itself up).

You can set repetitions for full and partial backups (in days and times, and only on weekend if desired), and it will automatically put your instance in maintenance mode (so no DB corruption) do its pass, release maintenance mode and do all the compression/splitting/uploading then, so there's as little down-time as necessary.

Seems well thought out, if possibly a little early in development!