https://www.bountysource.com/?search=duplicati seems to do that (found while trying site out).
You can see that the median cumulative bounty on the issues list is $20, so effectiveness is not much. Some of the (few) volunteer developers can’t even accept token amounts due to employer restrictions.
Duplicati team doesn’t run the site, so not much point sending feature requests for Bountysource here.
There’s quite possibly not even formal affiliation. These folks just fetch issues from GitHub themselves.
Bountysource pocketing people’s money? was a recent ugly decision they made then retracted quickly.
You can certainly open feature requests just like this one, saying exactly what you mean, and pointing to any solutions from other sources that do what you want. Forum feature requests get no pledge system, however they might get more community discussion. Perhaps someone will even offer a script solution.
If you want to spend money, you might find someone who’s good with scripts to writes scripts Duplicati could run by its scripting options. That’s usually how integration with databases gets done, and often it’s because there are few DB-vendor-supported ways to do backups. You don’t want to hack out your own.
Chapter 25. Backup and Restore from the PostgreSQL 12 manual describes how to pg-dump. Back up what that makes. If needed later, restore the backup and run psql. Admittedly there are manual steps… duplicati-client would be one way to automate, but a simpler might be to run Duplicati from a CLI script.