For “really important” files, you should have a remote copy in case a local disaster occurs.
You should also have multiple backups, and not rely solely on Duplicati, which is still Beta.
rclone would be one way to do that manually, even remotely.
There are lots of sync programs around, but sync risks sync of file damage from malware.
You should either have to manually do an action, or have some way to undo any damage.
If you try rclone to remote, unattended, –backup-dir might give you a way to do such undo.
Syncthing versioning might also do. See old post Duplicati vs. Syncthing (with versioning).
Office 365 version of OneDrive also has recovery to previous time, for malware protection.
I don’t use any of above because my needs are different, Yours is sort of a special case…