Ver. 1.79 now supports full screen!
Hold [Alt] and press [Enter].
After much trial and error, we have decided to deprecate 2K (1080p) excess.
The main reason for this is that it will be difficult for older PCs to enjoy the video in excess of 2K.
In order to allow as many people as possible to enjoy the game, we have no choice but to deprecate it.
Thank you for your understanding.