Screen display fills entire page

All of a sudden I can’t play my favorite game

because when I click on the game’s icon on the desktop, it fills the whole page with the icon but doesn’t turn on the game

I used to be able to play the game just by clicking the icon, now all I get is a big picture of the icon

how do I go back to non-page filling apps, I want to play my game!

I can’t find anything in settings that is called “display” that someone said controls this feature and can turn it back