This feature request has been declined.
Currently if you have the Teams app set to run in the background upon clicking the “X” in the upper right, the app stays active only in the system tray. If you receive chat messages, it still remains in the SysTray.
However, if you get an @mention, the focus pulls it to the Taskbar. This is by design since you are getting directly mentioned and some action is typically expected. This is a key design element which the team does not wish to deviate from.
We appreciate the suggestion but will respectively decline it at this time.
Thank you for the feedback and suggestion.
-WarrenDanny Bertisen commented
So far every update has caused the app to open.
That should not happen, the app should not be that agressive.
Also keeping minimized through GPO would be highly desired.