Apple does not supporting UISplitViewController.DisplayMode .PrimaryOnly as splitViewController.preferredDisplayMode

apple does not support 'UISplitViewController.DisplayMode.PrimaryOnly'.

How can enable the masterViewController as UISplitViewController.preferredDisplayMode (UISplitViewController.DisplayMode.PrimaryOnly) on higher-end iPhone devices (such as iPhone 14 Plus) in landscape mode?

I am utilizing a splitView with the style .doubleColumn. My objective is to have the splitView present the MasterView as the initial screen and the Detailed view as the subsequent screen in landscape mode, resembling the default iPhone portrait mode, specifically on higher-end iPhone devices (such as iPhone 14 Plus and iPhone Pro Max). If launched on an iPad, it should be displayed as 'side by side' ('oneBesideSecondary').

How can we display the MasterViewController using splitViewController.preferredDisplayMode, specifically setting it to UISplitViewController.DisplayMode.PrimaryOnly when rotated to landscape mode on iPhone higher end devices? However, it's important to note that Apple does not support UISplitViewController.DisplayMode.PrimaryOnly.

here is my code :

class ViewController: UIViewController , UISplitViewControllerDelegate {
    var splitVC = UISplitViewController(style: .doubleColumn)
   // var splitVC = UISplitViewController()
    var delegateProtocol : TableSelectionDelegate?
    var ListView : ListViewController!

    override func viewDidLoad() {
        splitVC.delegate = self
        splitVC.presentsWithGesture = true
        splitVC.preferredSplitBehavior = .tile
        ListView = ListViewController()
    override func viewWillAppear(_ animated: Bool) {
        var primaryVC : ListViewController = UIStoryboard(name: "Main", bundle:nil).instantiateViewController(withIdentifier: "ListViewController") as! ListViewController
        var secondVC : SecondViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController

        primaryVC.delegate = self
        secondVC.view.backgroundColor = UIColor.placeholderText
        if UIDevice.current.userInterfaceIdiom == .pad
            splitVC.setViewController(primaryVC, for: .primary)
            splitVC.setViewController(secondVC, for: .secondary)
            splitVC.preferredDisplayMode = UISplitViewController.DisplayMode.oneBesideSecondary
            splitVC.setViewController(secondVC, for: .primary)
            splitVC.setViewController(primaryVC, for: .secondary)
            splitVC.preferredDisplayMode =   UISplitViewController.DisplayMode.secondaryOnly
            // hide back btn to primary list
            let controllers = splitVC.viewControllers
            primaryVC = (controllers[controllers.count-1] as! UINavigationController).topViewController
            as!  ListViewController
            primaryVC.navigationItem.leftBarButtonItem =
            primaryVC.navigationItem.leftItemsSupplementBackButton = false
        splitVC.view.frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.height)
        splitVC.didMove(toParent: self)
    func splitViewController(_ svc: UISplitViewController, willChangeTo displayMode: UISplitViewController.DisplayMode) {
        if UIDevice.current.userInterfaceIdiom == .phone
            svc.presentsWithGesture = displayMode != .secondaryOnly

extension ViewController : TableSelectionDelegate
    func selectedRow(row: Int, viewController: UIViewController) {
        splitVC.showDetailViewController(viewController, sender: self)

I attempted the code above by swapping the PrimaryVC with .secondary and the SecondaryVC with .primary in the splitView for the iPhone device type. As a result, I achieved the desired UI.

splitVC.setViewController(secondVC, for: .primary) splitVC.setViewController(primaryVC, for: .secondary) splitVC.preferredDisplayMode = UISplitViewController.DisplayMode.secondaryOnly.

However, I'm uncertain whether this approach was correct or incorrect. What would be the best approach to achieve my desired UI?

Desired UI:
iPhone Portrait : 

![Simulator Screenshot - iPhone 14 Plus - 2023-12-07 at 18.06.30|231x500](upload://hhW04y7ogBP2VejJimX4FnbNE7l.png)

![Screenshot 2023-12-07 at 6.40.54 PM|232x500](upload://zZl8TPZrgUSAC8fXz3ARX1O9OYS.jpeg)

iPhone Landscape : 
![Simulator Screenshot - iPhone 14 Plus - 2023-12-07 at 18.07.55|690x318](upload://1OgB1PQuIjWp8ZFtTudiQrSbTqY.png)

![Simulator Screenshot - iPhone 14 Plus - 2023-12-07 at 18.08.01|690x318](upload://8HAOPdmsGtfp7KweyxC8c3YgeTw.png)

iPad :
![Simulator Screenshot - iPad Pro (11-inch) (4th generation) - 2023-12-07 at 18.09.17|349x500](upload://1BYjNBfrkmqVKLHpuNIpIuRv6pY.jpeg)

![Simulator Screenshot - iPad Pro (11-inch) (4th generation) - 2023-12-07 at 18.09.25|690x481](upload://2MqsnEKGZMa84rd5OabmHbyvjS9.jpeg)

Questions that are specific to Apple app development or the use of Apple frameworks should be asked on the Apple developer forums.