What do you mean? Like muting the entire application so no sound comes from Teams or muting yourself while on a call? For the latter, I thought 'Option + Space' worked (or used to)?
I think GP is asking about a global (from any application) mute/unmute teams Mic. I have wished for one for ever.
Is completely muting your mic sufficient? If so, I have an Applescript solution that seems to work if you want it. I tested it in VoiceMemos and it worked even if I was in a different app in a different space. You can bind the script to a global hotkey very easily via many different apps like Alfred, Karabiner, etc..
AppleScript: https://pastebin.com/xHE1uQym