Another interesting thing.
If I open it up with 'sudo' in Terminal
sudo /Applications/OBS.app/Contents/MacOS/OBS
It opens an instance that is a blank. In other words, needs setting up again. No projects in place. Completly blank.
Menu bar items worked,. Seemed fine.
It doesn't appear to wipe out your existing settings because I closed it, and opened another instance with just open,
open /Applications/OBS.app/Contents/MacOS/OBS
and there were all my running settings again. But again, no working menu bar.
So really, this is a Catalina Permissions problem I reckon. Or in large part anyway.
Thank you! This worked! I'll be recording to try to see if it works later this weekend.