I've found the problem with the Fullscreen button, it's due to having enabled the option "Enable itch.io Sandbox".
https://itch.io/docs/itch/using/sandbox.html
Enabling this option makes the Fullscreen toggle malfunction in your game.
However, now i've tried your game while Windowed, on resolutions with aspect ratio's less than the width of 16:9, a part of the UI is cut off as the game tries to scale outside the window.
The bottommost resolution option (1920 x 1080 | 60) doesn't do anything, while one option higher (1920 x 1080 | 59) does change the window size.