you can always present another UIView on top of the SKiew however the scene will keep getting events.
[self.view addSubview:[[UIView alloc]initWithFrame:self.view.bounds]]
or you can present a full view controller on top. the key here is setting the modalPresentationStyle to UIModalPresentationCurrentContext and this will keep the current ViewControler and the Scene running in the background.
UIViewController *uivc = [[UIViewController alloc] init];
[uivc.view setBackgroundColor:[[UIColor clearColor] colorWithAlphaComponent:0.5]];
self.scene.view.window.rootViewController.modalPresentationStyle = UIModalPresentationCurrentContext;
[self.scene.view.window.rootViewController presentViewController:uivc animated:YES completion:nil];
(setting the background color is just for you to see the view)