I'm running Fedora 42 and have built the following based on the rpmfusion.org packages and updating snapshots:
After configuring v4l2-relayd to actually start doing something useful, all Cheese and Camera see are all-black. mpv kind of hangs and doesn't even open a window. qcam sees nothing. firefox (via Google Meet) sees the camera, but ends up acting as if nothing is there.