When I went, some people were jeans and tshirts, some were fancy dress...its up to you...
Informal but semi formal works if you wish to, not required.
Based on decor inside ship when i went in 2008/food prices and types of people on cruise (couples and older crowd/when i went) we opted to be semi formal and i was glad we did most everyone on our specific cruise/sunset/dinner one-were formal or semi formal despite the agency saying it was optional/not needed to dress up. Side note; inside ship for dancing and dinner it was quite classy so again for me i was glad to be semi formal. At that time i was mid 20s and we were about the youngest on ship too so that was a bit uncomfortable for us (most were 40-50yrs old it seemed).
Not really, you can go casual to semi-formal
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