I don't understand most of the negative comments in this thread along the lines of "if my company would require I use Teams I'd quite on the spot". Really? an IM client is what's going to make you quit? I always thought it was amusing that old developers were super anal about vim vs emacs and saw it as a tongue in cheek but now I realize most of those people are really serious and take these things quite emotionally.…
It's a tool that people use day-in, day-out for all their communication with colleagues. If it's unpleasant to use, the majority of your work becomes a constant reminder of that unpleasantness.
I'd never quit on the spot though, I'd silently search for another job.