not getting navigationController?.pushViewController to work but present does?

I do have a non-Storyboard, 100% coded UIViewController, UICollectionView and UICollectionViewCell - works perfect.

here's the code in question:

SceneDelegate not sure if this is relevant, tho.

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

        guard let windowScene = (scene as? UIWindowScene) else { return }
        window = UIWindow(windowScene: windowScene)

        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        let myController = MyViewController(collectionViewLayout: layout)
        window?.rootViewController = myController
        window?.makeKeyAndVisible()
    }
.
.

ViewController very simple and straight forward...

class MyViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
    let data = loadOnboardingData()
.
.
override func viewDidLoad() {
        super.viewDidLoad()

        collectionView?.backgroundColor = .white
        collectionView?.register(MyPageCell.self, forCellWithReuseIdentifier: "cellId")
        collectionView?.isPagingEnabled = true
        collectionView.showsHorizontalScrollIndicator = false
        collectionView?.tag = myPageControl.currentPage

        setupMyPageControl()

    }

ViewControllerExtention here's the problem: the pushViewController method just doesn't do anything but the modal present works like a charm and I'm not getting what's wrong and why:

extension MyViewController: MyPageCellDelegate {
.
.
func didTabOnActionButton(title: String) {


        let storyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
        guard let homeViewController = storyboard.instantiateViewController(withIdentifier: "HomeViewController") as? HomeViewController else {
            print("Coun't find controller")
            return
        }
        navigationController?.pushViewController(homeViewController, animated: true) <- NO EFFECT
        //present(homeViewController, animated: true, completion: nil) <- WORKS PERFECT!

    }

MyPageCell I set up the Delegate via protocol and it seems that's fine too

protocol MyPageCellDelegate {
    func didTabOnActionButton(title: String)
}

class MyPageCell: UICollectionViewCell {

    var delegate: MyPageCellDelegate?

let myActionButton: UIButton = {
        let button = UIButton(type: .system)
        return button
    }()

myActionButton.addTarget(self, action: #selector(self.doAction), for: .touchUpInside)
.
.
@objc private func doAction(_ sende: Any) {
        delegate?.didTabEndOnboardingActionButton(title: "end Onboarding")
    }

so, any Idea what's wrong with:

navigationController?.pushViewController(homeViewController, animated: true)

EDIT --------------------------------------------------------------------

As pointed out by @Michcio this here: window?.rootViewController = UINavigationController(rootViewController: myController) works half way and as far as I understand it, I'm embedding myController into an UINavigationController which adds the Navigation Bar to the current and following controllers.

But that's not what I need!

What I need is a clean and simple one for the onboarding i.e. MyViewController and the HomeViewController should be one with a Tab- and Navigation Bar

Basically starting from scratch after onboarding.

I used to solve this in the previous version editing the AppDelegate first Method like this (in this example I used Storyboards):

extension AppDelegate {

    func showOnboarding() {
        if let window = UIApplication.shared.keyWindow, let onboardingViewController = UIStoryboard(name: "Onboarding", bundle: nil).instantiateInitialViewController() as? OnboardingViewController {
            onboardingViewController.delegate = self
            window.rootViewController = onboardingViewController
        }
    }

    func hideOnboarding() {
        if let window = UIApplication.shared.keyWindow, let mainViewController = UIStoryboard(name: "Main", bundle: nil).instantiateInitialViewController() {
            mainViewController.view.frame = window.bounds
            UIView.transition(with: window, duration: 0.5, options: .transitionCrossDissolve, animations: {
                window.rootViewController = mainViewController
            }, completion: nil)
        }
    }
}

and in the Delegate itself like this:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let isFirstRun = true // logic to determine goes here
    if isFirstRun {
        showOnboarding()
    }
    return true
}

but I'm seriously not getting the new SceneDelegate or simply don't understand it

Really would appreciate if someone could past some code here for re-use.