Based on some early user feedback, we are tracking an issue where the game insistently exists fullscreen mode.  We are engaging with the reporting player and will have an update as soon as we possibly can.

In the meantime, it may be effective to push either F-4 or ALT-ENTER if the game is not in fullscreen mode on launch. 

As a two person dev team, we have limited resources but we want you to know it is very personally important to us that you all have the best experience possible.