Adding a close button when presenting a Unified SDK ViewController modally

AddCloseButton.swift

private var backButton: UIBarButtonItem {
    let barButtonItem = UIBarButtonItem(title: "Dismiss", style: .plain, target: self, action: #selector(dismissViewController))
    if #available(iOS 13, *) {
        barButtonItem.image = UIImage(systemName: "xmark")
    }
    return barButtonItem
}

@objc private func dismissViewController() {
    navigationController?.dismiss(animated: true, completion: nil)
}

viewController.navigationItem.leftBarButtonItem = backButton