According to the update, guests on these longer cruises will be required to take a PCR COVID-19 test prior to debarking the ship on their final day. Here is what the Disney Cruise Line website says:
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Debarkation Day COVID-19 Testing: All Guests (adults and children, regardless of age) on 5-night and longer sailings are required to undergo a PCR COVID-19 test administered by Inspire Diagnostics on the ship prior to debarking. A $65 test fee will be charged to the folio of all Guests 12 years and older. Guests under 12 years of age will be tested at no charge. However, Guests booked on 5-night and longer sailings who choose to provide proof of vaccination will not be required to take a COVID-19 test upon debarkation.