Navigation controllers do not display in fullscreen anymore, but overlaid, somewhat similar to popover controllers. You can also pull the whole controller down to dismiss it.
Interestingly, Apple has introduced a new setting and changed the default behaviour.
If you want the old behaviour, you need to modify the code. The workaround is fairly simple:
let viewController = ...
let navController = UINavigationController(rootViewController: viewController)
if #available(iOS 13.0, *) {
navController.modalPresentationStyle = .fullScreen
}
self.present(navController, animated: true, completion: nil)
Still, backward compatibility, grumble, grumble...
