If you have already downloaded Fortnite to your Apple device, then it will work, but now you won’t be able to get any new updates from the developers as Apple has terminated the App Store account which was used to support Fortnite.
Apple Unplugs Fortnite Creator Account

Just a week ago, Epic warned all iOS and macOS users that, soon they would not be able to update Fortnite game after 28th August. John Voorhees, the Managing Editor of MacStories, shared this news on Twitter. He also said that App Store is highing PUBG, the Competitor of Fortnite.
You missed your chance. Epic is off the App Store now. Also, this fight has gotten very petty. Today’s featured app? PUBG https://t.co/evp2R6qRxC pic.twitter.com/2vyRj6Oy1U — John Voorhees (@johnvoorhees) August 28, 2020