Updated

From iOS 13, apps can have multiple active windows, so you need to access the window you want. So you can access a window of any View like this:

self.view.window

if you really want to access the UISceneDelegate you can access it like:

self.view.window.windowScene.delegate

Old: and NOT recommended:

Assuming

1. there is only one scene delegate.
2. There is only one scene and one window.
3. All view controllers in the app are all part of that one scene and its window.

You can implement a helper variable in SceneDelegate like this:

private(set) static var shared: SceneDelegate?

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

    guard let _ = (scene as? UIWindowScene) else { return }
    Self.shared = self
}

then you can access it anywhere like this:

SceneDelegate.shared?.window // or anything else