How to stop Microsoft Teams from opening on startup 

There are several ways to stop Teams from opening on startup but we’ve chosen the simplest, most direct technique. Note that you can use this method to stop any app from starting at launch.

1. Click on the magnifying glass icon next to the Start icon on the taskbar.

2. Type "settings" in the search bar then click on Settings.

3. Type "apps" in the search bar on the upper left. Select Startup Apps.

4. Scroll down until you find Microsoft Teams and toggle it off.