Don’t think you’d want to use the DB name as that can change, thought about using backup name as the prefix but again would be cumbersome if you renamed the job.
Maybe ask for a job prefix on the backup job setup and ensure it’s unique across jobs? Won’t help if you have multiple sources all pointed at the same place though.
Also this defeats one of the strengths of Duplicati which is you can loose everything and so long as you have the remote files you can restore. You can still restore if the prefix is non-standard but would be an extra hurdle that might confuse the less tech savvy.
Maybe it’d be better to have Duplicati check for existing files when setting up a new backup job and prompt with a warning if it finds some? “Warning: It looks like there are already existing files in this location, are you sure you want to continue etc. etc.?”