Your Mac hears the call, not the room

The other side is taken from the Mac’s own audio with a Core Audio process tap, not from a microphone pointed at your speakers. There is nothing to install and no output device to re-route: your volume keys keep working, and muting the Mac does not silence the transcript.

Your own voice rides a separate channel on the microphone. That separation is what lets the debrief know which half of the call was yours.