创建UINavigationController或UITabBarController时出现空白屏，求排查方案

尝试以编程方式在应用首页添加UINavigationController和UITabBarController，已尝试多种方法仍无法解决。代码先后放在SceneDelegate和AppDelegate文件中均无效果，严格按照教程编写代码后，运行模拟器仅显示空白屏，与教程效果不符。以下是当前SceneDelegate中的代码，恳请帮忙排查是否有遗漏要点：

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let windowScene = (scene as? UIWindowScene) else { return }
        // ViewController1()  ViewController2()
        let mainView = UINavigationController(rootViewController: ViewController())
        let VC1 = UINavigationController(rootViewController: ViewController1())
        let VC2 = UINavigationController(rootViewController: ViewController2())
        let tab = UITabBarController()
        tab.viewControllers = [VC1, VC2, mainView]
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.windowScene = windowScene
        window?.rootViewController = tab
        window?.makeKeyAndVisible()
    }
}

内容的提问来源于stack exchange，提问作者sdweh