Should UISceneSizeRestriction be available on iPhone in iOS 27?

I'm trying to require a minimum size in my UIKit-based iOS app. I added code to set that using the UIWindowScene.sizeRestrictions property to my app's scene delegate as recommended in Apple's documentation:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let currentScene = (scene as? UIWindowScene) else { return }
        
        currentScene.sizeRestrictions?.minimumSize.height = 400
        currentScene.sizeRestrictions?.minimumSize.width = 320
        
        print("*** Size restrictions: \(String(describing: currentScene.sizeRestrictions))")
 ...
}

When I run that in the simulator for an iOS 27 iPhone, the size restrictions property prints out as being nil. That's surprising to me, since the documentation states that "The system provides this object only when it supports variable-sized windows.", and iPhone windows are resizable in iOS 27.

If this is working as expected, is there another way to restrict the size of an iPhone window in iOS 27?