Does it matter how the ship is flagged? I could imagine solutions like, "If you dock in Europe and your ship is out of compliance, you must pay $X in fines." You can tune $X to whatever is needed to cover the calculated negative externalities.
But nothing regulates what they do in international waters.
The problem would be that if one country enacted a ban, all the ships registered there would just switch to some other country without the ban (or that usually skipped that inspection), and the original country would lose out on a bunch of much-needed cash.
It might be more effective to tax the dirty fuel at the source, so that it becomes uneconomical to the ship operators to use the dirty fuel in the first place.
"A ship that has burned X dirty fuel shall be charged $Y Euros per liter burned. If a ship is found to have created fraudulent logs, it shall be charged $Y*10, or seized. There is a reward for reporting such fraud leading to seizure equal to 10% of the forfeiture."
Or something like that. As long as the penalty is financially meaningful compared to the income of the ship's engineer, you would quickly start to have trouble getting away with using such fuel.
What you need to do is put the foot down and prevent flags of convenience (or more specifically, those that fail to meet environmental standards) from docking at your ports at all. Which I'm not sure is permissible under maritime laws.
(or maybe there is some dodge like preventing the ship from "carrying hazmat" which you define as bunker fuel, or ban ships from having soot in their stacks that has sulfur deposits, or so on...)
Its a hard battle to "force" any of these cruise lines or shipping for that matter, to change. It would have to be a EU law, etc etc, but thats 5+ (probably 10+) years to get passed.
Your ship may be registered to a tiny little island that won't enforce any regulation, but there's a limited number of markets to underwrite the insurance you need, and you'll want to dock at major sea ports.
[0] https://uk.reuters.com/article/us-shipping-fuel-sulphur/new-...
Cruiseships have been ignored for a long time because tourism=money.
As originally conceived the Paris MOU was about labour standards. European ports didn't like the fact that "Flags of Convenience" (legally, "Open Register" countries, where you can register a ship without any relationship to that country) were allowing ships in their register to have crew that weren't meeting European labour standards. Long working hours, poor pay, no healthcare and so on.
But by coincidence, as the meeting to sign the MOU was starting a terrible accident happened. Suddenly the headlines were about this nasty shipping accident, and you've got a bunch of people in Paris negotiating a new international agreement, so... today the Paris MOU is very interested in safety, with worker rights being a subsidiary consideration (after all if you're at the end of your fourth 16 hour shift this week you're probably not terribly safe if you're even still awake) but it also created this idea of Port State Control now seen in similar institutions around the world.
The US already de facto exercises Port State Control, and has laws which effectively bar foreign ships from doing a lot of stuff in US territory anyway - it could make a pollution regulation today if it cared, which obviously at least the Trump administration does not. But PSC wasn't really a thing anywhere else before the Paris MOU.