Teams uses their own notification system (at least on macOS) which:

1) looks terrible

2) does not behave like a standard OS notification so you can't swipe on the trackpad to dismiss it nor does it appear on the lockscreen (if your system is configured to display notifications on it)

3) is an always-open window (though invisible when not in use) but it still appears in the "window" menu and you can focus on it (seriously WTF? why not just create the window when a notification is displayed and destroy it right after)

4) takes up a lot more space while not delivering any more information than what a standard system notification would deliver