I find it really fascinating who gets it or who doesn't. I've been on 5 cruises since cruising restarted and I didn't get Covid on board either.
The first 4 cruises were with masks everywhere - I mostly used 3 layer cloth masks. I also tried to social distance whenever I could. Took the stairs as often as I could (but held on to railings, as I have problems with my knees and I don't want to fall down the stairs) and washed hands in the toilets, going into the shops and dining areas, as well as if there was a hand sanitizing station on entry to bars etc.
The last cruise was with no mandatory face masks (other than Embarking and disembarking) and I did the same thing with washing hands, social distanced etc. I did carry a face mask everywhere, in case I felt the need to wear one, but I never did.
I have had Covid but got it on land, with 2 vaccinations plus one booster.