Mic switching from webcam to internal during calls

Hi, I have an MacBook Air (M1, 2020). I started using it for work only in the last month, and have begun to have a problem during video meetings. I have a webcam and remote monitor, so I have the webcam as camera and the laptop speakers as my speakers. All starts out fine, but then out of nowhere the mic will switch over to the laptop mic (which is off because the laptop is closed). So I lose audio. I have to go back into the settings and switch back (and my webcam mic is always available).

This didn't happen initially, but seems to have been happening more often in the last couple of weeks. I'm typically on google meet and chrome. I've tried 2 different cameras and a range of different port configurations. I've googled this a bunch, but can't find anything.

Any ideas?