Sanger, as I said, this involves leaving a Schengen country, going to a non-Schengen country, and then returning to a Schengen country. As your own reference states:
"On the other hand, US residents coming from countries that have not established a visa-free regime with the EU will have to apply for a Schengen visa in the US, in order to be able to enter any of these countries."
Also, the info sent from the cruise company states, "A multiple entry visa will be required if a non-Schengen country is visited in between visits to Schengen countries. (Example: depart from Italy, visit Turkey, arrive in Spain)." My situation exactly.
This will be a deal-breaker for us. But I just can't believe that thousands of other people on the ship are going to do this. And I go back to my example where we were all set to go to from Spain to Morocco back to Spain last year and none of this came up.
BTW, this is an entirely separate issue from the ETIAS authorization, which is not a big problem for me. The multiple entry visa, on the other hand, involves a fee of $90 X 2, providing bank statements, submitting passport photos, and obtaining insurance, apparently over and above what the cruise line provides.