For our April Explorer cruise around Japan, we cleared the waitlist in August and found for many ports all tours were waitlisted or not even available for waitlist.
Over time, five ports had waitlists open up and we were able to get tours we were happy with, even if not our first choice.
There was one small port that had no tours ever become available, wasn’t a bad miss for us.
In Okinawa, if you can get into the Bingata Experience tour, we thought it was fun. YMMV