The crew on the cruises I have been on, were wearing the high quality KN95 (or similar) masks, so pretty effective.
Personally, I always felt that requiring crew to wear masks when cleaning empty cabins, or serving drinks on outside decks was unnecessary.
However, if I was a crew member working in an environment that entailed face to face interaction (customer services, bar staff with customers sitting at the bar), I think I would be inclined to carry on wearing them.