The game uses 2D backgrounds.
Either your video card or your monitor will have to handle whether it displays "full screen" because the game doesn't seem to have that capability.
A high end card like the GeForce GTX 1070 should have drivers that allow settings for individual games, and the capability to scale a game with a fixed 1280x720 resolution to a 4k resolution.
It's from last year, but here's a description of what's in Nvidia Control Panel
https://us.download.nvidia.com/Windows/382.33/382.33-nvidia-control-panel-quick-start-guide.pdf