Remove Navigation Controller behavior from one View

How will you get out of A4 ?

You can remove the segue that connects to A4.
Then in the button in A3 that previously led to A4, you should instantiate A4.
let newController = storyboard?.instantiateViewController(withIdentifier: "A4") as ? ClassForA4

Do you just want to hide the back button ?

If you want to hide the Back button:

• create a specific class for A4

• in viewDidLoad, hide the button

Code Block 
class ViewController4: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        self.navigationItem.setHidesBackButton(true, animated: true)
	}
}

I want a to do a popover window and that works if I have no Navgation Controller, because the new View appears over the old one.
B1->B2
If I set the background color of B2 to Clear Color and put a Label with a blue background color on it. The program does what I want. The tricky part now is that I want to include this simple behavior to my project, which needs a NavController.

Your explanations between different posts are really confusing.

Please clarify what you want exactly.

• Will B1 -> B2 be included in the TabBar ?

• Is B2 the popover window ?

• How is it called from B1 ? A button ?

I want a to do a popover window
So, why don't you simply

• create a UIView in B1

• set it as hidden in IB

• when to tap the button, just unhide the view

• propose a way to hid back the view (either a button or simply when tapping on the view)

That would be much simpler than create a B2 VC

If that works, don't forget to close the thread by marking this as correct answer.
Otherwise, explain precisely what you want to achieve.

Sorry, I am not very good at explaining my problem. But your first answer works really good, after a few difficulties. Thank you, the solution was much simpler than I thought it could be

TabBarController->NavController->A1->A2->A3->A4

Better try something like this:

Code Block 
->TabBarController->NavController->A1->A2->A3+
           |                                 ↓Trigger the transition from TabBarController to A4
           +---------------------------------->A4

Code Block 
import UIKit
class A3ViewController: UIViewController {
    
    @IBAction func buttonTapped(_ sender: UIButton) {
        let a4VC = self.storyboard?.instantiateViewController(identifier: "A4ViewController") as! A4ViewController
        a4VC.modalPresentationStyle = .fullScreen
        self.tabBarController?.present(a4VC, animated: true, completion: nil)
    }
}

(You may need to modify your storyboard and/or this code depending on your current project settings.)

@Luise_2020
Thanks for the feedback.
Did you use the UIView display option ?

Don't forget to close the thread on this correct answer.

Good continuation.