As you likely know iOS 13 introduced the multiple window concept. Which means what you used to do with
(UIApplication.shared.delegate as! AppDelegate).somevariableHERE
No longer works and I am happy to tell you that you can still do it just slightly different. And in my opinion clearer.
(self.window?.windowScene?.delegate as! SceneDelegate).someOtherVariableHere
Apple usual bare-extreme-bone docs