From the Royal Caribbean FAQ, https://www.royalcaribbean.com/faq/questions/international-ports-travel-considerations. The bolding is mine.
"What should I consider when booking a cruise visiting international ports?
Given the events over the last few years, having the proper travel documents has been a considerable concern of many guests prior to enjoying a carefree vacation. Passport, visa and inoculation regulations may vary by destination and may change from time to time. For your protection, your passport expiration date needs to be at least six (6) months after the sailing termination date. It is the sole responsibility of the guest to obtain and have available when necessary the appropriate valid travel and health documents such as passports, visas, vaccination certificates, etc., that are necessary for air travel, disembarkation at the various ports of call and re-entry into the appropriate country of origin."