Pasteboard

class ViewController: UIViewController {
    
    @IBOutlet weak var textView: UITextView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let pasteboardText = UIPasteboard.general.string ?? "Pasteboard is empty"
        textView.text = pasteboardText
    }


}

By enableing Secure Text Entry

Clear UIPasteBoard

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
        UIPasteboard.general.items = [[String: Any]()]
    }

Prepare your UI for the app snapshot

https://developer.apple.com/documentation/uikit/app_and_environment/scenes/preparing_your_ui_to_run_in_the_background

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationWillResignActive, object: nil, queue: OperationQueue.main) { _ in
            for view in self.view.subviews {
                if let textField = view as? UITextField {
                    textField.text = nil
                }
            }
        }
        
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        NotificationCenter.default.removeObserver(self)
        super.viewDidDisappear(animated)
    }

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    
    static var customPasteboard = UIPasteboard(name: UIPasteboardName(rawValue: "CustomPasteboard"), create: true)
    
    lazy var spashView: UIImageView = {
        let imageView = UIImageView(frame: self.window!.frame)
        imageView.backgroundColor = UIColor.green
        return imageView
    }()


    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
        
        self.window?.addSubview(spashView)
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
        spashView.removeFromSuperview()
    }