Milan 4 is far from sold out, still a few large sections of expensive standard price seats unsold: U2 ASSAGO 16/10/18 Tickets - TicketOne https://www.ticketmaster.it/it/event/u2-experience-innocence-tour/1489
Couldn't find that link on the website, it was just saying register for news about the tickets so I presumed it was sold out. Yeah on the map there 4 blocks with good availability