Trying to follow along a tutorial, but AddForce(ForceMode2D.Impulse) doesnt work

I have tried everything, and it definitly has to do something with ForceMode.Impulse, because a) the Condition triggers, b) ForceMode2D.Force works.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Playero : MonoBehaviour{
 
 
        public float runSpeed;
        private Rigidbody2D myPlayer;
        private Vector3 change;
        public bool isGrounded = false;
        public bool isGrounded2 = false;
        
        
        void Start () {
               myPlayer = GetComponent<Rigidbody2D>();
        }
 
        void Update () { 
               change = Vector3.zero;
               change.x =  Input.GetAxisRaw("Horizontal") * runSpeed;
        }
           
        void FixedUpdate (){
               Jump();
               myPlayer.MovePosition(
                      transform.position + change * runSpeed * Time.fixedDeltaTime
               );
        }
 
        void Jump(){
               if (Input.GetButtonDown("Jump") && isGrounded == true){
                      myPlayer.AddForce(new Vector2(0f, 500f), ForceMode2D.Impulse);
               }
        }
 }