Just saw this on the website for the Duomo complex and thought I'd pass it along for readers currently able to travel to Florence. I'm guessing that at least the new fee structure will likely stick once visitors from banned countries are allowed into Italy again. On the other hand, opening days/hours and maybe reservation processes could (and likely will) change.
They've overhauled the website for this family of attractions:
https://duomo.firenze.it/en/home
https://operaduomofirenze.skiperformance.com/en/store#/en/support/faq
It appears that the previous comprehensive ticket (€ 18 per adult; € 3 reduced) is history, almost all of the attractions within the group now have a separate entry fee, and each requires a separate reservation time. While the cathedral itself is still free, it currently requires a (free) reservation time as well. It's possible they'll come up with a new all-inclusive ticket down the road but that's a wait-and-see.
Briefly, current adult prices are as follows:
https://operaduomofirenze.skiperformance.com/en/store#/en/support/prices
Museum and Baptistry combined ticket: € 10,00
Bell Tower: € 15,00
Dome: € 20,00
Terraces (available by escorted tour only): € 25,00
Current visiting hours/days are much more restrictive that they were formerly (Example: Museum/Baptistry/Cathedral only open Sat, Sun and Mon) but I'm sure those will expand as tourism opens up.
https://operaduomofirenze.skiperformance.com/en/store#/en/support/service
Due to ongoing restrictions regarding Florence attractions in general, Firenzecard (which can be of questionable value to begin with) has temporarily suspended sales.
http://www.firenzecard.it/en
Anyway, just a friendly reminder for folks doing trip research that info in previous posts or current guidebooks can, and likely will, change with the COVID situation. It's especially important to reference an attraction's own website for the most timely information, OK?
Editing to add: if on a tight budget, my personal value pick for a singular ticket would be the baptistry/museum combo.