I've got a headscratcher with my camera setup on macOS Monterey. I go back and forth between using an external webcam (a Logitech C615) and the internal FaceTime camera on my MacBook Pro. I've had zero issues for the entire time I've had the laptop. A week ago, I updated to Monterey from Catalina, and now both cameras are behaving very strangely.
First, the actual camera functionality on the webcam failed, but the laptop still detects it as a microphone. I tried plugging in the webcam through docks, directly via a USB-C->A dongle, etc., and it did not work. I figured the camera had died, so I bought a brand new one and it did not work either. However, I noticed something very weird when I plugged in the new camera. If I open FaceTime with no webcam plugged in, I can see that the internal camera works. However, as soon as I plug in the external camera, the internal camera fails to be detected with the message "no camera connected", and of course the webcam does not work either. FaceTime can see the microphone on the webcam but suddenly does not recognize the internal MacBook Pro camera or the external one. ~50% of the time, restarting FaceTime after unplugging the camera works and restores the internal camera. Sometimes, it requires a reboot.
What I've tried
As described above, I tried every dongle/direct plug I had, as well as trying a new webcam. I manually stopped and restarted the video controller via
sudo killall VDCAssistant. I've reset the
PRAM and the
SMC. I've booted into Safe Mode and replicated the problem there. I fully updated macOS to the latest version (12.2.1) and updated all of the component software. I tried to reinstall macOS via Recovery Mode, but was unable to connect to the Internet for some reason and was unable to complete the update. I've tried installing ManyCam per the solution in this StackExchange question which did not work.
Any ideas on what might be causing this? What should I do from here? Please let me know if there is any other info I can provide, either about the system or the webcam.