If they do the same as they do on Musica, then they change the Buffet area into a chargable Bistro for evening dining.
The buffet is free of charge but be advised if they operate in line with the rest of their fleet, this closes in the evening. They do have an additional Italian Restaurant on this ship which is chargeable. The formal restaurant, as you refer to it, is only Formal on 2 nights of the cruise. Other nights are smart casual. Go on to MSC website/ships/Poesia/dining, all the info is there. Regards Wilba.