ctrl + shift + m for mute in Teams
Presumably the GUI focus group testing they did showed that space used everywhere else is too complicated for users so they went for something simpler.
I mean, WTF. Who decided on that? I didn't even know it existed. I just randomly tried hitting space every few months thinking they'd finally get round to putting it in in an update. It turns out they had, but you'd need a safe cracker to find it.