>To pause/quit the game, you need to enter full screen for some reason.
I think the WebPlayer version gets drawn over by the itch.io quickmenu on the side.
I had the same issue that I couldn't pause/give up, then widened the window (on a 1920px wide monitor) and managed to pause - Only thing that changed was the position of the "View all by Alarts / Follow / Add to collection..." quick actions.