he could be anyone one of us

i think you may be misunderstanding how the auto-detect size feature on itch works: it does not make itch resize the canvas/iframe to match the window size, it just uses the detected game dimensions as the fixed size without you having to enter them manually. this template will make the game's canvas resize to fit any iframe that contains it, but it does not affect how itch resizes those iframes on the game page.
if you have a 1920x1080 game, i'd recommend one of the following: