iOS / iPadOS only backup strategy

Note: Sync is ​not ​a backup, neither advertised nor advocated as such. A backup should be application agnostic and file-based. Sync uses raw, chunked, and optionally encrypted data only for use with DEVONthink and DEVONthink To Go.

DEVONthink To Go cannot sync to a local sync store.
Due to iOS’ backups not allowing for individual file restorations, you can use sync as an ad-hoc backup but that is not the intended use of syncing.