Will be visiting Florence for Christmas and I understand many things will be closed on Christmas eve and Christmas day. Any thoughts on what we absolutely need to see? Planning a day trip to Castello Rocchetta.
I don’t remember things being closed in Florence at Christmas Eve when I lived there (or when I visited at Christmas time). As a matter of fact, it is a very busy shopping day and the historical center is packed (at least before pandemics). But yes, on Christmas Day many things are closed (like stores) although many restaurants open at least in the historical center (outside the city center nearly everything closes).
High Mass inside the Duomo on the night of the 24th of December is in my opinion a must, regardless whether you are a Catholic or not. On Christmas Day most Italians have a belly bursting luncheon with the family at home, but eventually in the afternoon, people come out to take a stroll or go to the movies (although the latter may be restricted due to Covid). Some churches may have free organ concerts as well.
Xmas eve is a working day in Italy, but some things may close earlier than usual. I hope you did not learn that many things are closed on Steves' books.