If you mean on the game preferences, why you cant get it full screen? Renpy, although safe to use, causes alarms with anti viruses. Ive noticed this when I tried interacting with trying to save a game as well as trying to go full screen. Had to redownload the whole thing because Avast broke it (on other games though). Try checking your anti virus for things it has (recently) blocked. If it's not that IDK what it could be.