title: Why is Linking.getInitialURL always returning null?
body: <p>I'm successfully using deep linking to open my app from a share extension. If the app is already running, then I get the information in <code>ComponentDidMount</code> using <code>Linking.addEventListener('url', this.handleOpenURL);</code> </p>
  
  <p>If the app isn't already running, I expect to be able to use <code>Linking.getInitialURL();</code> per the docs (<a href="https://facebook.github.io/react-native/docs/linking" rel="noreferrer">https://facebook.github.io/react-native/docs/linking</a>). Except it is always coming up <code>null</code> for me. The link is how my app is being opened, but no matter what, comes out as null. I have that code in componentDidMount in App.js. </p>
  
  <p>I'm on react-native 59.2. </p>
  
  <p>Here is my AppDelegate.m </p>
  
  <pre><code>#import "AppDelegate.h"
  
  #import &lt;React/RCTBundleURLProvider.h&gt;
  #import &lt;React/RCTRootView.h&gt;
  #import &lt;React/RCTLinkingManager.h&gt;
  
  @implementation AppDelegate
  
  - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
    NSURL *jsCodeLocation;
  
    jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
  
    RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
                                                        moduleName:@"MYMODULENAME"
                                                 initialProperties:nil
                                                     launchOptions:launchOptions];
    rootView.backgroundColor = [UIColor blackColor];
  
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UIViewController *rootViewController = [UIViewController new];
    rootViewController.view = rootView;
    self.window.rootViewController = rootViewController;
    [self.window makeKeyAndVisible];
    return YES;
  }
  
  - (BOOL)application:(UIApplication *)application
              openURL:(NSURL *)url
              options:(NSDictionary&lt;UIApplicationOpenURLOptionsKey,id&gt; *)options
  {
    return [RCTLinkingManager application:application openURL:url options:options];
  }
  
  - (BOOL)application:(UIApplication *)application continueUserActivity:(NSUserActivity *)userActivity
   restorationHandler:(void (^)(NSArray * _Nullable))restorationHandler
  {
    return [RCTLinkingManager application:application
                     continueUserActivity:userActivity
                       restorationHandler:restorationHandler];
  }
  
  @end
  
  </code></pre>
  
  <p>If the app is already running in background, <code>getInitialURL()</code> returns the link that launched it, otherwise I get null. I expect to get the link that launched the app even if it wasn't running.</p>