How many times do people post "what to do?" and "what to see?" in Italy? That is not a criticism but hopefully this will help people with their trip planning.
While researching my September trip to Northern Italy I found this website https://www.italybyevents.com/en It covers much of Italy and allows search by region, location (city), month for lists of things to do and see. There are links to the events' and sights' websites for more information; it does not appear to be a third party booking site. It does not include the major sights but focuses on the smaller events and sights.
Enjoy your adventure! Buon Viaggio!!