Correct sequence of loading UISplitViewController from the storyboard manually

MYAppDelegate.m

#import "MYAppDelegate.h"

@interface MYAppDelegate () <UISplitViewControllerDelegate>
/...
@property (nonatomic, strong) UISplitViewController* splitViewController;
@end

@implementation MYAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    // ...
    
    // loading initial vc the way many folks around do
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:[NSBundle mainBundle]];
    UIViewController *vc =[storyboard instantiateInitialViewController];
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = vc;
    
    // set up split vc
    self.splitViewController = (UISplitViewController *)self.window.rootViewController;
    UINavigationController *navigationController = [self.splitViewController.viewControllers lastObject];
    navigationController.topViewController.navigationItem.leftBarButtonItem = self.splitViewController.displayModeButtonItem;
    navigationController.topViewController.navigationItem.leftItemsSupplementBackButton = YES;
    self.splitViewController.delegate = self;
    self.splitViewController.preferredDisplayMode = UISplitViewControllerDisplayModeAllVisible;
    self.splitViewController.preferredPrimaryColumnWidthFraction = 0.5;
    // do any other split vc customization if needed
    
    // this is an important part: call this _after_ split vc set up, otherwise you'd get wrong collapsed vc presented by split vc
    [self.window makeKeyAndVisible];
    
    // ...
    
    return YES;
}

@end