We just released our first patch to JTL. Okay, technically it's the 5th one, but the others were all for really odd things (like accidentally shipping the game with a completed file, oops!

This patch adds the option to Toggle Full Screen on the main menu's Option section:

After hitting the toggle, you'll see the game shrink from Full Screen to a Windowed screen. When hitting the toggle, the game just tries adopting the highest resolution your monitor supports. We tried building the UI to anchor to sections of the screen you'd expect them to, but you might want to practice some restraint with wild aspect ratios because you might not see important bits in cut scenes or some UI elements might look weird. Still, we didn't think locking the aspect ratio was strictly necessary so if something works better for you, give it a try!

Thanks for all of your support!