Using Storyboard programmatically as main storyboard

Load_ViewController_from_AppDelegate.swift

/**

AppDelegate.swift
In Project settings set the "Main Interface" text field to empty.

With the Interface Builder implementation, 
the app launches the initial view controller of the storyboard set in the target’s Main Interface.

To do something similar in code, you need to take a different approach.
Open AppDelegate.swift and replace the code inside application(_:didFinishLaunchingWithOptions:) with the following:”
*/

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
  var window: UIWindow?
  
  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
    
    // Initialize the storyboard in code using the storyboard name
    let storyboard = UIStoryboard(name: "TabBar", bundle: nil)
    
    // Create a reference to the storyboard's initial view controller
    let viewController = storyboard.instantiateInitialViewController()
    
    // Set the app delegate's `window` using the device's screen size as the `frame`
    window = UIWindow(frame: UIScreen.main.bounds)
    
    // Set the window's  root view controller to the storyboard's final view controller
    window?.rootViewController = viewController
    
    // By calling `makeKeyAndVisible()` on your window, window is shown and positioned in front of every window in your app. For the most part, you''ll only need to work with one window.
    //There are instances where you'd want to create new windows to display your app's content.
    // Example an external display in your app.
    window?.makeKeyAndVisible()
    return true
  }
}