I believe you should have upgraded your Xcode to version 11 and make your app compatible with iOS 13. But just a reminder about a recent announcement of Apple
iOS 13 is now running on 77% of all iOS devices introduced in the last four years, worldwide. Deliver great user experiences by seamlessly integrating with Dark Mode, Sign in with Apple, and the latest advances in ARKit 3, Core ML 3, and Siri. Starting April 30, 2020, all iPhone apps submitted to the App Store must be built with the iOS 13 SDK or later.
So, please make sure you use the iOS 13 SDK to build your apps and keep enjoying the tutorials we collected for you.
By the way, we’ve updated our Mastering SwiftUI book with a new chapter that teaches you how to work with JSON, Slider, and data filtering with SwiftUI. If you love to learn SwiftUI, you can check out the book here