I just installed the release candidate last night, and now most apps can't capture my webcam's full resolution. It's a Logitech C615, and it supports 1080P 30fps, but only over MJPEG. Now apps are either capturing incredibly choppy video, or capturing at the low resolutions the camera supports over RGB.
12.3 RC no longer supporting MJPEG webcam capture
This was fixed eventually, and is at least working properly by 12.4.
MJPEG support is broken since Monterey Beta and Monterey 12.0, and as of Monterey 12.6 it's not working properly. Most of the webcams cannot choose MJPEG on Monterey.