The line will continue to follow the travel requirements of the destinations it visits.
A country by country listing is here.
Greece, for example, still requires testing
Greece, for example, still requires a negative COVID-19 test for vaccinated and unvaccinated passengers 12 and older, or a certificate of recovery. The test may be antigen, taken within two days before embarkation, or PCR, taken taken within three days before. Self-administered tests are not accepted.