Great resources. I actually found those as well and unfortunately the problem must lie with the new FaceTime app itself.
The webcam is a newer Nexigo camera and works in other applications. In FaceTime, I’m able to select the correct camera from video settings when I but just displays as black with no option to make calls, etc (like it’s stuck loading). After a while it gives an error message that the camera couldn’t load and that I should try restarting my computer. The internal MacBook Pro camera works with no issues. After a restart of the app and computer, still no dice.
I had no problem until the recent updates to the OS and FaceTime. OS X Big Sur was working with the older FaceTime version.