Most embedded microphones these days are digital MEMS microphones, using PDM. For those, if you gate off the digital signal, it's gone for good. I wouldn't be surprised if this is what Apple is doing.

This is how the Google Home Mini does it. When you flip the mute switch, an AND gate kills the digital signal from both microphones (a stereo microphone pair share a single data line). All the audio hardware gets is a string of 0 bits at that point.