rigidybody.velocity doesn't work anymore

Scripting
1

rigidybody.velocity doesn’t work anymore, they’d said that GetComponent().velocity works instead that, but doesn’t.

2

It works just fine here is an example.

using UnityEngine;

[RequireComponent(typeof(Rigidbody))]
public class Jump : MonoBehaviour
{
    public float jumpForce = 10f;

    private bool isJumping;
    private Rigidbody rb;

    // Awake is called when the script instance is being loaded
    void Awake()
    {
        rb = GetComponent<Rigidbody>();
    }

    // Update is called every frame, if the MonoBehaviour is enabled
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            isJumping = true;
        }
    }

    // This function is called every fixed framerate frame, if the MonoBehaviour is enabled
    void FixedUpdate()
    {
        if (isJumping)
        {
            rb.velocity = Vector3.up * jumpForce;
            isJumping = false;
        }
    }
}