Chrome is the new IE in terms of support. "Best viewed in Chrome"
Safari is the new IE in terms of weird bugs that no other browser encounters. Some of their web APIs like LocalStorage and IndexedDB still have odd quirks (but at least they're not completely broken any more).
Ye, i remember they mentioning this, and people i know confirm it works fine. It just doesnt work on my end. I do have firefox set up to be very private though ( no 3th party cookies and more )
That's definitely a part of it. All of the MS web platforms rely heavily on first and third party cookies. You can't even log in properly to Teams if your browser is in incognito/private mode.