When you mute on Facetime on MacOS, it highlights the microphone button. But when you mute on Facetime on iOS, then it does the opposite by unhighlighting the microphone button. Why Apple?!?!!? You have no idea how many times I failed to mute my farts as a result because of this inconsistency.
Mute buttons are a pure peeve of mine. If you haven't already definitely send this to https://www.apple.com/feedback (I don't use FaceTime much but I bitch to Microsoft about the same thing in Teams.)