Nav + State

public extension View {
    func navigationAppearance1(standardAppearance: NavigationBarAppearance,
                               scrollAppearance: NavigationBarAppearance,
                               currentAppearance: Binding<NavigationBarAppearance>) -> some View {
        modifier(NavigationAppearanceViewModifier1(standardAppearance: standardAppearance,
                                                   scrollAppearance: scrollAppearance,
                                                   currentAppearance: currentAppearance))
    }
}

private struct NavigationAppearanceViewModifier1: ViewModifier {
    let standardAppearance: NavigationBarAppearance
    let scrollAppearance: NavigationBarAppearance
    @Binding var currentAppearance: NavigationBarAppearance

    func body(content: Content) -> some View {
        content.background(NavigationAppearanceRepresentable1(standardAppearance: standardAppearance,
                                                              scrollAppearance: scrollAppearance,
                                                              currentAppearance: $currentAppearance))
    }
}

private struct NavigationAppearanceRepresentable1: UIViewControllerRepresentable {
    let standardAppearance: NavigationBarAppearance
    let scrollAppearance: NavigationBarAppearance
    @Binding var currentAppearance: NavigationBarAppearance

    func makeUIViewController(
        context: UIViewControllerRepresentableContext<NavigationAppearanceRepresentable1>
    ) -> NavigationAppearanceViewController1 {
        let viewController = NavigationAppearanceViewController1(standardAppearance: standardAppearance,
                                                                 scrollAppearance: scrollAppearance)
        viewController.onAppearanceChange = { appearance in
            currentAppearance = appearance
        }
        return viewController
    }

    func updateUIViewController(
        _ uiViewController: NavigationAppearanceViewController1,
        context: UIViewControllerRepresentableContext<NavigationAppearanceRepresentable1>
    ) {
        uiViewController.update(standardAppearance: standardAppearance, scrollAppearance: scrollAppearance)
    }
}

private final class NavigationAppearanceViewController1: UIViewController {
    let standardAppearance: NavigationBarAppearance
    let scrollAppearance: NavigationBarAppearance
    var onAppearanceChange: ((NavigationBarAppearance) -> Void)?

    init(standardAppearance: NavigationBarAppearance,
         scrollAppearance: NavigationBarAppearance) {
        self.standardAppearance = standardAppearance
        self.scrollAppearance = scrollAppearance
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        if let navigationController = navigationController {
            navigationController.style(standardAppearance: standardAppearance, scrollAppearance: scrollAppearance)
            onAppearanceChange?(standardAppearance)
        }
    }

    func update(standardAppearance: NavigationBarAppearance,
                scrollAppearance: NavigationBarAppearance) {
        if let navigationController = navigationController {
            navigationController.style(standardAppearance: standardAppearance, scrollAppearance: scrollAppearance)
            onAppearanceChange?(scrollAppearance)
        }
    }
}