Baffled me too but I get it now, they want fullscreen on the first monitor and a clock on the second.
Thankfully, these days when I want to play a bit (with a computer, sigh) on my Sway setup, yeah, it doesn’t react to that button.
Saying all that, yeah, I never considered that — having your game being lost to buggy and slow Windows — a feature. I wouldn’t want that even today, having 125 times more RAM than 20 years ago.