As I am learning more and more about SwiftUI and iOS app development in general, I am coming to the conclusion that it currently is impossible to build a high fidelity app by only using SwiftUI for the UI layer. The SwiftUI API coverage is way too limited and immature to build anything that is more complex or customized than the projects Apple demos at WWDC. Of course it is possible to build high fidelity apps with the help of SwiftUI, but from my perspective this requires learning how to use UIKit and integrating it with SwiftUI views.
This year ist the first year after Apple first released SwiftUI. When I look at what features and APIs will be released this fall I guess that it will take another 2 to 3 years till SwiftUI is mature enough to completely rely on it. Till then new Swift developers like me have to swallow the bitter pill and learn UIKit.