I'm speculating here, but maybe there are better controls in Big Sur to easily mute input devices compared to prior versions of OSX. I've attempted building a global microphone mute app (for external microphones) on Catalina but never found an easy way to fully mute all mics such as external USB mics or a those connected through a USB ADC. The best I could get on Catalina was to lower the inputVolume to 0 which does not truly mute the microphone. I never found an app that "solved" this problem for all microphones on OSX versions prior to Big Sur.