He’s a southsider from what I heard earlier.
He's from the south suburbs of Chicago, very close to where the Blues Brothers are canonically from. This is the part of Chicagoland where people unironically speak with the "Superfans" accent. If you look at his early biography, what churches he attended, where he went to school, etc., you could not write a more stereotypical biography of a White Sox fan. So I would be surprised if he turns out to be a Cubs fan.
That said, I am a White Sox fan from the North Side of Chicago so I am in no position at all to throw the first stone if this Pope bleeds Cubbie blue. Or frankly to show my face in public at all, given the last two years.