Typically 2 Formal Nights on a 7 night cruise where casual is not acceptable & the rest of the cruise Smart Casual.
Formal means formal. Suit and tie please. Don't be sloppy.
I've not sailed with MSC Cruises but you'll probably find most men in black tie amd women in long or cocktail dresses, though a lounge suit and shirt and tie are usually acceptable.
We have been with MSC several times, you can be as formal as you want to be, last time hubby didn't take a tux or a tie, and we were not out of place - it was relaxed and fabulous. We were still invited to dine with the Captain and to the exclusives cocktail party, and if we had worn 'full blown' formal - we would have been the only ones.