I think that is a choice for the individual.
My wife and I caught Covid on our last (Arcadia) cruise, presumbaly contracted on board, but possibly in a bar or restaurant ashore.
On our cruise, which was only half full, mask wearing was well enforced, but even so there were some cases of Covid towards the end of the cruise.
There is only one way to be 100% sure of not contracting covid on a cruise, and that is not to get on the ship in the first place.