its actually says how on this page.
Q: How do I resize the game window? Sorry, but the game is forced to launch at 1280 x 720. If you want to make the game bigger: On windows: If you make a shortcut for "Max_The_Elf_DEMO", then go to properties of the shortcut, and add " -screen-width 1920 -screen-height 1080 -screen-fullscreen 1 " to the [target/destination (translated from dutch)] property, it will launch with those settings! Image preview: https://imgur.com/a/R4lV2Xn