Launching an Android application from within unity without extending UnityPlayerActivity?

The documentation : Launching an Android application from within unity describes how to extend the UnityPlayerActivity to call the Intent method, but I want to do it without extending UnityPlayerActivity, by simply calling a Java class. but I can't succeed doing that.

C# code :

 private static AndroidJavaClass ajc =new AndroidJavaClass ("com.MyCompany.AmazingApp.niceBuilder") ;
     
 AndroidJavaClass jc = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
 AndroidJavaObject jo = jc.GetStatic<AndroidJavaObject>("currentActivity");
     
 AndroidJavaClass  intent = ajc.CallStatic<AndroidJavaObject>("createIntent");
     
 jo.Call(startActivity,intent);

Java Code :

 public static Intent  createIntent(){
      Intent myIntent = new Intent();
      myIntent.setAction(Intent.ACTION_VIEW);
      myIntent.setData(android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI); 
      return myIntent;  
        }

I also tried to start the activity completely from inside createIntent().

java code :

 public static void createIntent(Activity currentActivity){
     Intent myIntent.setAction(Intent.ACTION_VIEW);
     myIntent.setData(android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI);
          
     currentActivity.startActivity(enableBtIntent);
 
     }

and then call the function from unity

 ajc.CallStatic<void>("createIntent",jo);

but nothing works. I quote from the documentation :

"This intent then needs to be setup in the onCreate function"

could that be the reason, if so why, why do I need to setup my Intent in onCreate()?, and is there any solution to this problem?