I'm pretty sure that macOS doesn't do this by default at all, based upon over a decade of experience. This StackOverflow seems to agree — but it also offers su

I'm pretty sure that macOS doesn't do this by default at all, based upon over a decade of experience. This StackOverflow seems to agree — but it also offers suggestions to help find the actual culprit (a lot of third-party software seems to auto-level the mic volume), and also offers a further suggestion of configuring an Aggregate Audio Device (using the default Audio MIDI Setup app) which doesn't have a mic-level control that apps can mess with. Perhaps one of the solutions discussed here might help you. https://apple.stackexchange.com/questions/97810/mac-osx-microphone-input-volume-level-auto-adjusts-can-it-be-disabled https://apple.stackexchange.com/questions/97810/mac-osx-micr...