Unity version of Mario jumping physics. If you get jump key down you jump higher than just a press

MarioJump.cs

// Source : https://www.youtube.com/watch?v=7KiK0Aqtmzc

#region Variables
[SerializeField] private float jumpVelocity = 5;
[SerializeField] private float fallOffMultiplier = 2.5f;
[SerializeField] private float lowJumpMultiplier = 2;

private Rigidbody2D rigidbody;
#endregion Variables

private void Jump (KeyCode jumpButton)
{
    if (Input.GetKeyDown (jumpButton))
    {
        rigidbody.velocity = Vector2.up * jumpVelocity;
    }

    if (rigidbody.velocity.y < 0)
    {
        rigidbody.velocity += Vector2.up * (Physics2D.gravity.y * rigidbody.gravityScale) * (fallOffMultiplier - 1) * Time.deltaTime;
    }
    else if (rigidbody.velocity.y > 0 && !Input.GetKey (jumpButton))
    {
        rigidbody.velocity += Vector2.up * (Physics2D.gravity.y * rigidbody.gravityScale) * (lowJumpMultiplier - 1) * Time.deltaTime;
    }
}