I got my buddy to install Screen and sent him a meeting link. When he opened it, he was on the call, and he could hear me, but his own mic wasn't functioning. I could see him muting and unmuting the mic via the icon, but no sound came through.
I noticed that when I installed Screen, it prompted me to allow Screen in the Security/Privacy settings for microphone access. Then when I started the call, it asked for permission to use the mic. My buddy didn't get prompted on install, and Screen doesn't appear in the list of apps that have requested microphone access. We wiped out his Application Support/Screen directory and reinstalled from scratch, but with the same result.