Have this issue as well. I reported this (FB11359136)

I just checked the code from the first post, but it seems to work here without any change 🤔 Xcode 14.0 beta 6 (14A5294g) in the iPhone 12 Pro simulator.

It seems SwiftUI ignores the UINavigationBarAppearance settings and doesn't have an API for changing/removing the bottom border indeed. There is also no API for forcing SwiftUI to use UINavigationBarAppearance. There only solution I found is removing the new iOS 16 API's (.toolbarBackground(..)) and use SwiftUI-Introspect to set the navigation appearance manually: .introspectNavigationController { controller in controller.navigationBar.compactAppearance = appearance controller.navigationBar.standardAppearance = appearance controller.navigationBar.scrollEdgeAppearance = appearance controller.navigationBar.compactScrollEdgeAppearance = appearance }