Object instantiates in the same spot (ScreenToWorldPoint)

Hi, I am trying to instantiate an object at the mouse x and y and a predefined z. This code instantiates the object at 0,1,-10 all the time, can anyone tell me the reason?

 void Update () {
         
         if(Input.GetMouseButtonDown(0)){
             Debug.Log("mouse clicked");    
             
             Vector3 mousePos;
             
             mousePos=Input.mousePosition;
             mousePos.y=4;
             mousePos.z=0;
             
             Vector3 worldPos;
             worldPos=Camera.main.ScreenToWorldPoint(mousePos);
             
             Debug.Log(worldPos);
             Instantiate(b,worldPos,Quaternion.identity);
             
         
         }