We ended an Airbnb for two nights in Florence. What should we do while we’re there?
Do you have a guide book?
Read RS Italy tours for some great ideas on must sees. Mine are the Baptistry and the Uffizi and the Covered Bridge for great shopping. If you want to buy souvenirs and have time there are some Outlets across the River. Go early in the morning to the famous places. It's a wondeful place just to walk around and record scenic vistas.
2 nights = 1 full day. The exact date of that one full day is important as most museums are closed at least one day a week. A guidebook is a very good start for gathering ideas which appeal to your own interests.
Click on this link: https://www.ricksteves.com/europe/italy/florence. Scroll down to the At a Glance section and click on the + sign on the right.
Accademia and the Uffizi are closed on Mondays. The Duomo is open seven days a week.
The duomo website states that it's closed to visitors (sightseers) on Sundays.
https://duomo.firenze.it/en/discover/cathedral
Lots of suggestions here: