I have the same question- more specifically, it would be ideal if MFMailComposeViewController "just worked" with whatever the default email client was, for example setting recipients, subject, body, etc.

Just want to share my attempt which also had no luck navigationController?.navigationBar.topItem?.backBarButtonItem = UIBarButtonItem(title: "Back", image: nil, primaryAction: action, menu: menu) This successfully changes the title (navigationItem?.backBarButtonItem does not) but my custom action and menu are ignored- the primaryAction is still to pop and the menu still shows the navigation stack.

Thanks for the quick response- can you clarify, if I submit an update will the extension be removed even for users running iOS 13 and earlier?