In MacOS 14.1 / Sonoma, Apple has removed support for legacy camera and video system extensions which means that OBS can no longer find the device for recording.
Luckily the fix is quite simple:
1/ Shut down your computer 2/ Hold down the power button for Macs using Apple Silicon or hold CMD + R for Intel Macs. 3/ When presented with the Recovery Mode click on the Options icon 4/ Select Utilities, then Terminal 5/ Enter the command below and hit Enter/Return:
6/ Quit terminal and Restart the device.
Note: If using encryption you may need to unlock the drive before being able to run the command above.