I’m American, but my ethnicity would be Italian. We have Festa Italiana which used to be an enormous event. Unfortunately due to many issues with the board of directors and an aging [off the boat] Italian population it’s probably 50% of what it used to be. Looks like they do about 100,000 people, but they have a good half of the grounds blocked off (I assume the rent is higher if more is open).
Those grounds also host Polish Fest, German Fest, Irish Fest, Mexican Fiesta, and a handful of others. There’s also smaller ones scattered around the city throughout the summer.
Milwaukee does have a good sized German and Mexican population and enough Italians to warrant a large festival, however, everyone goes to whatever festivals they want. Or rather, they go to whatever festivals they want food from. Beyond going to them for the music/concerts, restaurants throughout the city have booths there. So you can go to Festa and just about every Italian restaurant in the city will have a presence.