I don't know .... I visited Milano many years ago and then again in 2015. We didn't have that long there, just long enough to return the rental car, have a night at a hotel close to the Duomo, have a meal at the Galleria and walk around a while. We didn't get to many of the recommended sites/sights, and not to La Scala, so I can't comment on too many landmarks.
I know many people speak highly of Milano and no doubt they have seen many wonderful things there ... everyone's experience is not the same .... fortunately.
map courtesy of wikipedia
What a building! The interior was relatively standard, smart in typical Italianate-style. The opportunity to clamber over and around the dome was spectacular. There is a short [expensive] elevator ride to the top once you can find it [it's way round the back and not that well sign-posted] but if you have to be in Milano you should take the time to visit and take the elevator to the top and spend time up there enjoying the view over the city and the carvings ... it is just spectacular!