If you have multiple cameras (e.g., built-in + external USB webcam) and apps keep picking the wrong one, disable the camera you don’t want to use.
In the Camera settings, you can also:
(This GUID corresponds to camera devices.)
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\DeviceClasses\65e8773d-8f56-11d0-a3b9-00a0c9223196