mac OS microphone only works when using Siri, works fine on bootcamp
I had the same issue recently, and i found a seemingly stupid fix to it.

Go to system preferences, keyboard, and access the dictation and try using it on any document. The default to using dictation on my mac was double tapping Fn button. Strangely enough my dictation feature worked and typed what i spoke on the screen as Siri did. Then, go back to your input devices and check if that "permanently" fixed ur input issue; microphone should now also work without dictation being active.