Probably a recent thing, now it takes total control of the display and you can’t do anything else while waiting for the match to start. Only exception being you already opened your browser so you can alt-tab into it but now while the game is running you don’t have the access to desktop. Is there a way to go back to the previous state where you can simply alt-tab out?
I think its because you are running the game in fullscreen. If you want to go to desktop you can press Windows Key + D . You can also press the window key once to open the start menu and open an app there.