Hello! I had the same issue with installation of Sonoma on my Mac. I found a work-around from Apple to allow the system to recognize virtual cameras again. Sonoma had a security ‘upgrade’ that creates the issue we are experiencing here. ManyCam on Zoom is functioning as it had in the past once I followed these easy steps from Apple.
I have a month full of virtual workshops and this saved me from having a boring old school Zoom training. 