We spent Christmas in Sicily in 2012. The week leading up to that was in Rome, the week after was in Sorrento and surrounding area. Every Italian city and town was decorated with lights, some suspended over the streets. Presepi (manger scenes) are abundant, too. If you’re going to museums, double check for hours of operation.
Rome - We arrived at the Vatican Museums right after they opened one morning, and although there was a long velvet rope maze outside the entrance to handle crowds, we were the only ones there, and marched right inside. The museum got more full as the day went on, but we had an hour with very few others at the beginning. The Sistine Chapel wasn’t very crowded when we reached it, although there was a long, long line that afternoon waiting to reach security to get into St. Peter’s. Weather was in the lower 50’s during the day - cool but not cold. A jacket was sometimes needed, but not a heavy coat.
Sicily - we stayed at an Agriturismo Christmas Eve and Day. There was a huge lunch there Christmas Day, then things wound down and were quiet the rest of the day and evening. Seemed people spent the day with their families, and it wasn’t a day to go out and about on other activities.
Sorrento/Naples/Amalfi coast/Pompeii - week between Christmas and New Year’s, museums were open and had a fair number of visitors. Restaurants were busy. No dining outside at that time of year. At the stroke of midnight on New Year’s, the skies above Sorrento were filled with people’s personal fireworks displays for 20 minutes, then it settled down and was quiet the rest of the night. The next morning, we found out that the ruins at Pompeii, which were originally going to be closed all day, were going to be open until 1pm, a short day. We went, and except for a huge, loud Russian tour group, there was almost nobody else there. Again, check hours and open days, then recheck.
Our Rome trip planned for September 2020 got cancelled, as you’ve m experienced, but we’ve scheduled a new trip this coming late September, starting in Bologna. Hope our trip happens, and yours does, too!