UINavigationBarAppearance background does not extend to the top edge on iPhone Duo

Environment

• Xcode 27.1
• iOS 27.1
• iPhone Duo simulator
• UIKit app built with the iOS 27.1 SDK

Issue

On iPhone Duo, the background of a system-managed UINavigationBar does not extend completely to the top edge of the window.

The navigation bar is configured using UINavigationBarAppearance with an opaque blue background. However, a horizontal white strip remains above the blue navigation bar.

I also post a feedback: FB24859353

Questions

1. Is this expected behavior on iPhone Duo?
2. What is the recommended way to style this top region?
3. Should apps add a custom background underlay outside the UINavigationBar bounds?
4. Could this be an iOS 27.1 or iPhone Duo simulator issue?

Minimal reproduction code:

import UIKit

final class DemoTabBarController: UITabBarController {
    override func viewDidLoad() {
        super.viewDidLoad()

        viewControllers = NavigationBarStyle.allCases.map { style in
            let content = DiagnosticsViewController(style: style)
            let navigationController = UINavigationController(rootViewController: content)
            navigationController.tabBarItem = UITabBarItem(
                title: style.title,
                image: UIImage(systemName: style.symbolName),
                selectedImage: nil
            )
            style.apply(to: navigationController.navigationBar)
            return navigationController
        }
    }
}

enum NavigationBarStyle: CaseIterable {
    case systemDefault
    case appearance
    case legacy

    var title: String {
        switch self {
        case .systemDefault:
            return "Default"
        case .appearance:
            return "Appearance"
        case .legacy:
            return "Legacy"
        }
    }

    var symbolName: String {
        switch self {
        case .systemDefault:
            return "iphone"
        case .appearance:
            return "paintbrush"
        case .legacy:
            return "clock.arrow.circlepath"
        }
    }

    func apply(to navigationBar: UINavigationBar) {
        switch self {
        case .systemDefault:
            break

        case .appearance:
            let appearance = UINavigationBarAppearance()
            appearance.configureWithOpaqueBackground()
            appearance.backgroundColor = .demoBlue
            appearance.shadowColor = nil
            appearance.titleTextAttributes = [.foregroundColor: UIColor.white]
            navigationBar.tintColor = .white
            navigationBar.standardAppearance = appearance
            navigationBar.compactAppearance = appearance
            navigationBar.scrollEdgeAppearance = appearance

        case .legacy:
            navigationBar.tintColor = .white
            navigationBar.barTintColor = .demoBlue
            navigationBar.backgroundColor = .demoBlue
            navigationBar.setBackgroundImage(Self.solidImage(color: .demoBlue), for: .default)
            navigationBar.shadowImage = UIImage()
            navigationBar.isTranslucent = false
            navigationBar.titleTextAttributes = [.foregroundColor: UIColor.white]
        }
    }

    private static func solidImage(color: UIColor) -> UIImage {
        return UIGraphicsImageRenderer(size: CGSize(width: 1, height: 1)).image { context in
            color.setFill()
            context.fill(CGRect(x: 0, y: 0, width: 1, height: 1))
        }
    }
}

private extension UIColor {
    static let demoBlue = UIColor(red: 0.0, green: 0.46, blue: 0.70, alpha: 1.0)
}