Always - however the requirements will be for the port not the specific excursions the cruise can book
I think the real question here is if someone tried to use a fake vaccination card would they get away with it...
Dunno. One site I saw did go on about how illegal it is to use the CDC logo on something homemade Pretty sure that'd be copyright infringement not a federal felony but they're playing it up big time.
Absolutely does for concerts and other events. A friend made one for another friend who didn't have one. White out, a pen and a copy machine whipped it up right quick.
I honestly don't think anyone gives a rats ass anymore. Companies are just checking boxes to cover their ass and life goes on....