If you enter fullscreen over all monitors on macOS, then open options and reduce things to just one screen, then the second screen remains black and unusable until you leave fullscreen completely.
This issue has been fixed upstream by this commit:
Tested and can confirm that we no longer get unusable, black screens when going from fullscreen on all monitors to fullscreen on one monitor.
macOS 12.0 with 3 monitors.
Jenkins client build 2271 on macOS 12.0.
Jenkins server build 2355 on RHEL 8.
Steps to reproduce:
1. Open the client, go to Options -> Screen and select "All monitors" and make sure "Fullscreen mode" and "Enable fullscreen mode over all monitors" are enabled.
2. Log in.
3. Open Options (via F8). Under Screen, disable fullscreen mode over all monitors.
Instead of selecting "All monitors", I also tested selecting "Current monitor" and "Work area (maximized)". These give a black unusable area in the session (as intended), that disappears when doing step 3.
I could verify the issue using the 4.13.0 client on macOS 12. I could also verify that the issue is now fixed with a nightly client (build 2271) on the same macOS machine.
The "other" monitors no longer appear black once full screen on all monitors is deselected, and it is now possible to interact with the macOS desktop on those displays.