The topic isn’t valid anymore, I can connect to the core now. Though I couldn’t connect to the core right after the update. I had to reinstall roon core and restore everything from backup, then I was able to connect and change my music location from local to network share and now things are back to normal again.
So the problem description would be that local folders can’t be found in Roon for QNAP anymore after the 1.8.846 update. Would be nice to get confirmation if this is intentional or a bug, thanks.