iOS - Código para rodar sem Main.Storyboard

AppDelegate.swift

@UIApplicationMain //or @main
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow()
        window?.rootViewController = RootViewController()
        window?.makeKeyAndVisible()
    
        return true
    }
}

SceneDelegate.swift

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 }

        let window = UIWindow(windowScene: windowScene)
        window.rootViewController = RootViewController()
        self.window = window
        window.makeKeyAndVisible()
    }
}