Just an FYI, ManyCam 7.10.0.19 with macOS Monterey 12.3 (beta) does not work with two cameras of the same make/model. It will show two of them in ManyCam (e.g. “Logitech BRIO” & “Logitech BRIO (1)”), but only one is selectable. It will randomly choose one of the two and that’s the only camera you will be able to access. It seems to be because of the naming the OS gives them, but no other video program (MS Teams, FaceTime, Zoom, etc.) have any problems selecting between the two, just ManyCam.
(Just FYI, why I’m on 12.3 beta is because every time I launched Zoom and ManyCam I would have USB faults that would disconnect my cameras, USB mic, everything. I thought it was a hardware issue after I reinstalled macOS fresh and it did the same thing. Sent it to Apple for repair and they found nothing. Sure enough when I got it back, it’s only when I use ManyCam with Zoom it happens. If I use the cameras directly in Zoom, one or the other, it works just fine. So I’ve been trying the 12.3 beta to see if it works better with it. So far, no USB faults, but now having this problem of only being able to choose one of the two cameras again.)