Spawn from GameObject C#

So I have this code:

{

 public Transform prefab;
 public GameObject clickHere;
 
 private Transform spawn;
 private Rect rect = new Rect(161,227,545,75);
 
 void  Update()
 {
     if (Input.GetMouseButton(0) && spawn != null) 
     {
         var pos = Input.mousePosition;
         pos.z = -Camera.main.transform.position.z;
         spawn.transform.position = Camera.main.ScreenToWorldPoint(pos);
     }
     
     if (Input.GetMouseButtonUp(0)) 
     {
         spawn = null;
     }
 }
 
 void OnGUI() 
 {
     Event e = Event.current;
     
     if (e.type == EventType.MouseDown && rect.Contains(e.mousePosition)) 
     {
         var pos = Input.mousePosition;
         pos.z = -Camera.main.transform.position.z;
         pos = Camera.main.ScreenToWorldPoint(pos);
         spawn = Instantiate(prefab, pos, Quaternion.identity) as Transform;
     }
     
     GUI.Button (rect, "Button");
 }

}

It does this:

1- Click the rectangle (there s a button so I can see where it is, it won t be in the future) 2- prefab spawns 3- While you hold the mouse button, you will drag the object

I wanted to spawn the prefab from a game object so I adjusted the rectangle to it, but I soon realized the rectangle will change it s position for different screen resolutions. So I would like the code to do the same but with the gameObject instead of the rectangle.