We sailed on the Mariner in May and I tested positive 2 days after getting home.
We just sailed on the Harmony two weeks ago and this time I did wear my N95 mask while standing in line to board and in the terminal. I also wore it every time I stepped on the elevator, in the Windjammer, when entering and leaving the shows and anytime I could see I was about to be in a close crowd. I also wore it at the end of the cruise to debark the ship.
Whether or not it helped or I just got lucky I do not know, but I felt like I was doing all I could to protect myself and neither my husband nor myself came down with covid this time.