This is a sample of Scene delegate methods, showing the basics of navigation in a project without StoryBoard. There are 2 ViewController files in the project: SearchBiewController & FavoritesViewController; each of them is embeded in a Navigation Controller

Navigation: Scene Delegate sample.swift

import UIKit

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 }
        
        // init window with the frameSize of the windowScene bounds
        window = UIWindow(frame: windowScene.coordinateSpace.bounds)
        
        //assign windowScene to window
        window?.windowScene = windowScene
        
        //assign the root ViewController
        window?.rootViewController = createTabBar()
        
        // show the ViewController
        window?.makeKeyAndVisible()
    }
    
    
    /// Adds a Navigation controller for SearchViewController()
    func createSearchNavController() -> UINavigationController {
        let seachVC = SearchViewController()
        seachVC.title = "Search"
        seachVC.tabBarItem = UITabBarItem(tabBarSystemItem: .search, tag: 0)
        
        return UINavigationController(rootViewController: seachVC)
    }
    
    /// Adds a Navigation controller for FavoritesViewController()
    func createFavoritesNavController() -> UINavigationController {
        
        let favoritesVC = FavoritesViewController()
        favoritesVC.title = "Favorites"
        favoritesVC.tabBarItem = UITabBarItem(tabBarSystemItem: .favorites, tag: 1)
        
        let favNavController = UINavigationController(rootViewController: favoritesVC)
        return favNavController
        
    }
    
    /// Adds a TabBar controller & assigns the Navigation controllers to it
    func createTabBar() -> UITabBarController {
        let tabBar = UITabBarController()
        tabBar.viewControllers = [createSearchNavController(), createFavoritesNavController()]
        
        // adding tint color for TabBar
        UITabBar.appearance().tintColor = .systemTeal
        
        return tabBar
    }