Destroyer of the damned title unlock

Community rewards such as the "Destroyer of the Damned" title should be issued within 72 hours after being completed. If its still not there sometimes they wait to distribute certain rewards at the end of the event as well. I would wait until the even ends and if you don't see it 72 hours after that then I would send a support ticket to Rare to try and resolve the issue.

https://www.seaofthieves.com/fury-of-the-damned#faq-how-do-i-earn-and-claim-the-event-rewards