Microsoft Teams changed the way it notifies users of new/unread messages. Unfortunately, this caused users to stop receiving unread/new message notifications.
Here’s the fix:
- Open the Microsoft Teams application on your Mac
- On your keyboard, press command + comma
- Click Notifications in the left panel
- In the dropdown menu for Notification style in the right panel, select Mac
- A notification may pop up on the top right corner of your screen. Hover your mouse over it, click Options, and click Allow
And that should do it.
Microsoft tends to break things that ain't broke.