The version of the game posted on itch has significant bug where the game's UI breaks if it is not played on a screen that is in a 16:9 aspect ratio. Sorry about that, haven't bothered fixing the bug after posting the game back in 2021.
A quick google search yields that the mac you're using has a screen with an aspect ratio of 16:10. Playing the game in fullscreen in the browser may force a non-16:9 aspect ratio, consequently breaking the game.
Try playing the browser version in non-full screen, it may help, though I'm not completely sure.