Here's Seabourn's actual policy
After 6:00 p.m., suggested attire for all venues on board will be one of the following:
Resort Casual: Slacks and a sweater or shirt for men; sundress, skirt or slacks with a sweater or blouse for women. Jeans are not considered appropriate in The Restaurant.
Elegantly Casual: Slacks with a jacket over a sweater or shirt for men. Dress, skirt or pants with a sweater or blouse for women. Jeans are not considered appropriate in The Restaurant.
Formal Optional: While Elegantly Casual is always appropriate during the evening, a Formal Optional evening will be provided for guests who wish to dress more formally at least once each seven days. Formal Optional attire includes a tuxedo or dark suit with tie for men, cocktail dress or other formal apparel for women. On Formal Optional evenings, we request no jeans in any of the lounges or dining venues.
And please god tell me Seabourn has better spelling than "SOFHISTICATED FINE DINING AMBIANCE OF THE RESTAURANT..."
Regent is listing Elegant Casual as the dress code every night on the cruises I looked at. But of course if a guest wants to wear a tux, the line isn't going to stop them. It's an elegant ship.
I never mentioned Silversea's as dropping formal nights, so not sure where that came from.
And this isn't a debate about formal nights, some people love them which is great. This was a question if you liked then, tolerated then, or ate elsewhere to avoid them.