Quick test on adding subview to the window. We are making a label that when tapped creates a second dragging label. The dragging label is moveable around the screen. Then when you release the dragging view is removed and the label is updated.

FirtDraggableLabel.swift

/*
 FirtDraggableLabel, October 2021
 Quick test on adding subview to the window.
 We are making a label that when tapped creates a second dragging label.
 The dragging label is moveable around the screen.
 Then when you release the dragging view is removed and the label is updated.
 
 This project is also me remembering how UIKit UIWindows work.
 As well as adding subviews directly to UIWindows.
 
 UIKit, UIWindow, Popover, Draggable UI, Custom UIControl, iOS
 
*/
import UIKit
import PlaygroundSupport

// Use on screen
class MyViewController : UIViewController {
  override func loadView() {
    let view = UIView()
    view.backgroundColor = .white

    let dragLabel = DraggableLabel(frame: CGRect(x: 100, y: 200, width: 200, height: 50))
    view.addSubview(dragLabel)

    self.view = view
  }
}

class DraggableLabel: UIControl {
  
  /// First label that displays the label even when not interacting
  let label = UILabel()
  
  /// Second label that is popped into the window above all other elements
  let windowLabel = UILabel()
  
  /// Value set by interaction with dragging
  var sliderValue = 0.0
  
  required init?(coder: NSCoder) {
    fatalError("oops")
  }
  
  override init(frame: CGRect) {
    super.init(frame: frame)
    
    self.backgroundColor = UIColor(white: 0.1, alpha: 0.3)
    
    label.text = "I am at value \(sliderValue)"
    label.backgroundColor = UIColor(white: 0.0, alpha: 0.3)
    self.addSubview(label)
    
    windowLabel.text = "windowLabel"
    label.backgroundColor = UIColor(white: 0.0, alpha: 0.3)
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    label.frame = self.bounds
  }
  
  /// On touches begin we find the UIWindow and add the dragging subview to that window
  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    print("tap on")
    guard let window = self.window  else { return print("no window")}
    window.addSubview(windowLabel)
    windowLabel.frame = CGRect(x: 5, y: 5, width: 150, height: 50)
  }
  
  /// Everytime a touch changes, we update the position of the label and the value so it follows your finger
  override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touchOne = touches.first else { return }
    guard let window = self.window else { return }
    let location = touchOne.location(in: window)
    windowLabel.frame.origin = location
    windowLabel.text = "\(location.y)"
  }
  
  /// When touches are remove we clean up by setting the value to the static label and then removing the dragging label
  override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    print("tap off")
    label.text = "scrolled to \(windowLabel.frame.minY)"

    windowLabel.removeFromSuperview()
  }
    
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()
PlaygroundPage.current.needsIndefiniteExecution = true