As usually Celebrity gives two different statements
Testing Requirements
Pre-Arrival Covid-19 Testing
All guests ages 2 and older must present a digital or physical copy of a supervised, negative COVID-19 test result at check-in to board their sailing.
Guests must present a negative antigen test result taken within 2 days prior to sailing and no more than 2 days before their sailing.
Accepted tests are PCR or antigen tests taken in person, supervised virtually, or unsupervised self-administered. Proof of a negative test can be the printed or digital results, a clear photo of your self-test result, or your actual self-test in hand.