I went to the Milan derby last year (inter were the home side) signed up to a Siamo Noi card which cost €20 and got me priority, which for the derby was needed
worth noting I think since covid Italian teams have seen a rise in attendances , grounds used to be half empty but don't think that's the case anymore with the top teams (Roma for example)
san Siro is great and I urge you to get out there and do a game
good point above about taking ID that matches your ticket, that is absolutely vital and they won't let you in