If you have a positive PCR (not rapid) 11 days - 90 days before embarkation, with PCR positive date being day 0 as far as I understand - you can board with a certificate of recovery and no need for pre boarding test. Be aware that some ports will not allow you to disembark but you can get on the ship:
https://www.royalcaribbean.com/faq/questions/if-recovered-from-covid-19-need-to-be-vaccinated-or-take-a-test-to-sail