https://www.gamespot.com/articles/fortnite-battle-royale-42-content-update-now-avail/1100-6459119/

After months of being delayed, jetpacks have finally made their long-awaited debut in Fortnite: Battle Royale. The items arrive on PS4, Xbox One, PC, and iOS as part of the 4.2 content update, but despite their extended gestation period, they won't be around for very long.

Unlike most other items that Epic has recently added to Fortnite, jetpacks will only be available in the game for a limited time. The developer hasn't specified how long they'll appear, but you'll need to be pretty lucky to get your hands on one, as they're a Legendary item that can only be found in treasure chests.