If the camera isn’t working within the Microsoft Teams App, then you might need to look at the camera permissions. 

To do this, follow the steps:

1. Click on System Preferences. 

2. Go to Privacy & Security

3. Click "Microphone" > toggle ON Teams

4. Click on "Camera" > toggle ON Teams 

It's always good to do a device restart after makign the changes or close and reopen the Teams app.