Show the keyboard as a UISearchController in a modal is displayed

example.swift

class ViewController: UIViewController {

    @IBAction func onSearch(_ sender: Any) {
        let fakeWindow = UIWindow(windowScene: view.window!.windowScene!)
        let fakeTextField = UITextField()
        fakeTextField.autocorrectionType = .no
        fakeWindow.addSubview(fakeTextField)
        fakeWindow.makeKeyAndVisible()
        fakeTextField.becomeFirstResponder()

        present(SearchModalViewController(), animated: true) {
            fakeWindow.resignKey()
            fakeWindow.removeFromSuperview()
        }
    }

}

class SearchModalViewController: UITableViewController, UISearchResultsUpdating, UISearchControllerDelegate {

    private let searchController = UISearchController(searchResultsController: nil)

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
        searchController.obscuresBackgroundDuringPresentation = false
        searchController.delegate = self
        tableView.tableHeaderView = searchController.searchBar
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        searchController.isActive = true
    }

    func willPresentSearchController(_ searchController: UISearchController) {
        DispatchQueue.main.async {
            searchController.searchBar.becomeFirstResponder()
        }
    }

}