itch.io

Right clicking in the game with a mouse or long pressing on a touchscreen will show you the full screen option.

Llewelyn, check 9E, 9F, 9G in this Itch upload guide to make sure your game launches in fullscreen mode:

https://itch.io/jam/cavejam/topic/543846/tutorial-uploading-your-adventuron-game-to-itch