I wouldn't want to make that bet, considering a US keyboard has no AltGr key.

It might work with a US keyboard as long as your computer was configured for an Italian keyboard, though. https://en.wikipedia.org/wiki/AltGr_key suggests that from the keyboard's perspective, AltGr and right Alt are the same thing. Really, no keyboard allows any character -- they just send key codes (and modifier codes), and it's on your software to interpret those. But typing ² is not part of the normal, expected functioning of a US keyboard.

Edit: it occurs to me that perhaps I should gloss "it's on your software to interpret those" as "it is the responsibility of your software to interpret those".