How to layout view above Navigation controller using UIKit – Ios swift

I simulate your alert UIViews with my fake views because they aren’t in your code, I configure my navigation bar with my extension you can find it here: navigationBar Extension. For your goal you can use additional UIViewCintroller like this example:

In your SceneDelegate set your UINavigationController like that:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let windowScene = (scene as? UIWindowScene) else { return }
    window = UIWindow(windowScene: windowScene)
    window?.makeKeyAndVisible()
    let controller = UINavigationController(rootViewController: ViewController())
    window?.rootViewController = controller
}

After that configure you controller:

class ViewController: UIViewController {

let goButton: UIButton = {
    let button = UIButton()
    button.setTitle("Add", for: .normal)
    button.tintColor = .white
    button.titleLabel?.font = .systemFont(ofSize: 16, weight: .semibold)
    button.layer.cornerRadius = 12
    button.clipsToBounds = true
    button.translatesAutoresizingMaskIntoConstraints = false
    
    return button
}()

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .white
    
    setupNavigationBar()
}

private func setupNavigationBar() {
    
    let navBGColor = #colorLiteral(red: 0.3461649418, green: 0.3377231956, blue: 0.839216888, alpha: 1)
    configureNavigationBar(largeTitleColor: .white, backgoundColor: navBGColor, tintColor: .white, title: "ToDos", preferredLargeTitle: true) // my extension to configure navBar
    navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(addButtonTapped))
    navigationItem.rightBarButtonItem?.tintColor = .systemBackground
    
    goButton.backgroundColor = navBGColor
    goButton.addTarget(self, action: #selector(handleAlertDismiss), for: .touchUpInside)
}

// Dismiss your Custom Alert
@objc fileprivate func handleAlertDismiss() {
    self.dismiss(animated: true)
}

@objc private func addButtonTapped() {
    // Instantiate a new UIViewController for the alert
    let alertVC = UIViewController()
    alertVC.modalPresentationStyle = .overCurrentContext // present alertVC OVER current context 
    alertVC.modalTransitionStyle = .crossDissolve // with transition dissolve
    alertVC.view.backgroundColor = UIColor.black.withAlphaComponent(0.3)
    
    // Add the dimmed view to alertVC controller's view
    let dimmedView = UIView()
    dimmedView.translatesAutoresizingMaskIntoConstraints = false
    dimmedView.backgroundColor = .white
    dimmedView.layer.cornerRadius = 14
    
    alertVC.view.addSubview(dimmedView)
    dimmedView.centerXAnchor.constraint(equalTo: alertVC.view.centerXAnchor).isActive = true
    dimmedView.centerYAnchor.constraint(equalTo: alertVC.view.centerYAnchor).isActive = true
    dimmedView.heightAnchor.constraint(equalToConstant: 250).isActive = true
    dimmedView.widthAnchor.constraint(equalToConstant: 230).isActive = true
    
    dimmedView.addSubview(goButton)
    goButton.bottomAnchor.constraint(equalTo: dimmedView.bottomAnchor, constant: -10).isActive = true
    goButton.leadingAnchor.constraint(equalTo: dimmedView.leadingAnchor, constant: 10).isActive = true
    goButton.trailingAnchor.constraint(equalTo: dimmedView.trailingAnchor, constant: -10).isActive = true
    goButton.heightAnchor.constraint(equalToConstant: 40).isActive = true
    
    // Present the your custom Alert UIViewController
    present(alertVC, animated: true, completion: nil)
  }
}

This is the result:

When you tap on Add Button, alertVC dismiss itself for now… You can save your CoreData value in the handleAlertDismiss function.

UPDATE based on your comment:

remove closeButtonTap function from your DimmedView, remove closeButton.addTarget(self, action: #selector(closeButtonTap), for: .touchUpInside) from dimmedView. In ToDoViewContoller controller when create UIVievController add call to closeButtonTap function, move out of addButtonTap function constant alertVC and add the closeButtonTap function…

In ToDoViewContoller

let alertVC = UIViewController()

@objc private func addButtonTapped() {
alertVC.modalPresentationStyle = .overCurrentContext
alertVC.modalTransitionStyle = .crossDissolve
alertVC.view.backgroundColor = .black.withAlphaComponent(0.3) // declare here the bg color, remove it from DimmedView
let dimmedView = DimmedView()
dimmedView.translatesAutoresizingMaskIntoConstraints = false

alertVC.view.addSubview(dimmedView)
dimmedView.centerXAnchor.constraint(equalTo: alertVC.view.centerXAnchor).isActive = true
dimmedView.centerYAnchor.constraint(equalTo: alertVC.view.centerYAnchor).isActive = true
dimmedView.heightAnchor.constraint(equalTo: alertVC.view.heightAnchor).isActive = true
dimmedView.widthAnchor.constraint(equalTo: alertVC.view.widthAnchor).isActive = true

dimmedView.closeButton.addTarget(self, action: #selector(closeButtonTap), for: .touchUpInside)

 present(alertVC, animated: true)
}

@objc private func closeButtonTap() {
 alertVC.dismiss(animated: true)
}

In DimmedView class

override init(frame: CGRect) {
super.init(frame: frame)
//backgroundColor = .black.withAlphaComponent(0.3)
translatesAutoresizingMaskIntoConstraints = false
addSubview(customAlertView)
customAlertView.addSubview(label)
customAlertView.addSubview(textField)
customAlertView.addSubview(closeButton)
customAlertView.addSubview(addButton)
customAlertView.addSubview(detailsTextfield)
setUpConstraints()
}

Now when you tap X close button, alertVC go away…