Apple has banned the Fortnite mobile app from the iOS App Store, but there is still a way to install it or update it to the latest version if you had previously installed it. Epic Games recently modified its Fortnites mobile app to allow users to bypass Apple’s and Google’s app stores and buy vbucks directly from Epic at a reduced price. The move is against Apple’s policies as they earn 30% of all sales on in-app purchases, and led to the ban. With the ban, Epic Games quickly sued Apple and Google for monopolistic practices.
Source: https://www.bleepingcomputer.com/news/gaming/how-to-install-and-update-fortnite-on-ios-after-app-store-ban/