This is a known issue, and a fix is being worked on. It has to do with the scene collection ending up in a "corrupt" state if you have an unclean shutdown after removing a Video Capture Device source.

You should be able to resolve this in the meantime by loading the backup scene collection. You can do this by going into the ~/Library/Application Support/obs-studio/basic/scenes folder, removing the .json file for your scene collection, and then renaming the .bak file for the scene collection to just <your scene collection>.json.

If that does not resolve the issue, you should also be able to temporarily revoke the Camera permission from OBS, which will prevent the race condition from occurring on startup.

You should be able to resolve this in the meantime by loading the backup scene collection. You can do this by going into the ~/Library/Application Support/obs-studio/basic/scenes folder, removing the .json file for your scene collection, and then renaming the .bak file for the scene collection to just .json.

Unfortunately the recommended fixes don't resolve the issue for me. I still can't so much as open OBS, even when uninstalling/reinstalling and rebooting. Hoping that #11884 will provide a solution, when merged.

Update: I was able to resolve the issue by uninstalled OBS and deleting ~/Library/Application Support/obs-studio. I also rebooted, and had previously followed your instructions for revoking camera privileges (as well as video/audio). Not sure if those steps factored in.

Perhaps interestingly (perhaps not), OBS retains a key in ~/Library/Group Containers/group.com.apple.replayd/ScreenCaptureApprovals.plist after removing permissions via System Settings.