IBDesignable object does not render in IB inside a UITableViewCell

I have subclassed UIButton to get a checkbox :

let kCheckedImage = UIImage(named: "checked")!    
let kUncheckedImage = UIImage(named: "unchecked")!

@IBDesignable
class CheckBox: UIButton {
      @IBInspectable public var isChecked: Bool = false
  
    @IBInspectable public var image: UIImage?
  
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        image = kUncheckedImage
    }
  
    override init(frame: CGRect) {
        super.init(frame: frame)
     }
    
    override func draw(_ rect: CGRect) {
        image?.draw(in: rect)
    }
  
    override func awakeFromNib() {
        super.awakeFromNib()
        self.addTarget(self, action:#selector(buttonClicked(sender:)), for: UIControl.Event.touchUpInside)
    }
  
    @objc func buttonClicked(sender: UIButton) {
        if sender == self {
            isChecked = !isChecked
            if isChecked == true {
                    self.setImage(kCheckedImage, for: UIControl.State.normal)
            } else {
                self.setImage(kUncheckedImage, for: UIControl.State.normal)
            }
        }
        self.setNeedsDisplay()
    }
  
}

This works werll when I insert a CheckBox directly in a view in the storyboard.

Problam is when I try to inlcude such button in a xib (for UITableViewCell): the button works correctly, but I cannot get it drawn in IB.

I have tried to declare the UITableViewCell as IBDesignable, I have tried to include override func prepareForInterfaceBuilder(), no way.

Here is the code of the UITableViewCell associated to the xib:

class CheckCell: UITableViewCell {

    @IBOutlet weak var checked: CheckBox!   // The checked button
      
    override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code
    }
   
    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)

        // Configure the view for the selected state
       
    }
   
}