My mac says "Your screen is being observed" on the lock screen. How do I tell what app is doing this?? I've already turned off screen recording permissions for all apps in the Privacy section. And rebooted.

I mean is it driving a SDI matrix with multiple Hyperdecks? I mean it does appear to be being observed! Jokes aside, System Preferences > Security & Privacy > Screen Recording may give some clues.

Actually sounds you tried the second part, so it must know about your video setup…. 😃