This is probably much easier than you think! As Teams has unconsciously trained us to use hide button to hide chats and channels, it does not have a hide button for the control bar during a call.

To hide the control bar, which often blocks some contents, simply do not move your mouse! Or you could also move your mouse away from the application. The control bar will disappear after 2 seconds.

Honestly, they should also add a hide button in the control bar option! Agree?