I wouldn’t bother backing up the large, job-specific databases. Those can be recreated from the back end data, although a bug in how some older versions of Duplicati wrote dindex files can make that process painful. (There is a way to proactively fix that situation before you need to do a database recreate.)
Backing up the Duplicati-server.sqlite may be quite useful as it contains job definitions and other settings. Note that it contains credentials to back end storage so treat the file accordingly. I would just make a copy of it and store somewhere securely, don’t back it up with Duplicati itself. You can repeat the backup if you make any config changes.
Alternatively, you could export the job configurations to json format and store in a secure location. That’s what I actually do instead of backing up Duplicati-server.sqlite.