UITabBarController in UINavigationController

It can’t be done.

You can fake it by making your own tab controller, so long as you figure out a way to honor the surrounding UINavigationController, meaning a navigation bar atop and optional (disallowed?) tool bar below all tabbed views. 

Or you can use a modal segue to display the UITabBarController. That means:

  1. Convert the class to UIViewController.
  2. Make it implement UITabBarDelegate (if you wish). That means overridden delegate methods are no longer there to override.
  3. Create a fake UINavigationBar since you cannot embed thi

adding a navigation bar with a Done/Close bar button and perhaps an exit segue.