Rigidbody move at constant speed

Unity Engine
1

I am trying to move a character to the position of where the mouse was clicked. I tried using velocity, but it only moves until it’s velocity hits zero. How can I get a constant movement speed until the object reaches it’s destination?

Also, I want the character to move from 0 to max speed instantly and from max speed to 0 instantly as well.

Here is what I have tried:

    void Update(){
        int joysticks = Input.GetJoystickNames().Length;
        // No Joysticks attached, use Mouse
        if(joysticks < playerId){
            if(Input.GetMouseButtonDown(1)){
                Plane playerPlane = new Plane(Vector3.up, transform.position);
                Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
              
                float hitdist = 0f;
                if (playerPlane.Raycast(ray, out hitdist)){
                    Vector3 targetPoint = ray.GetPoint(hitdist);
                    var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
                    transform.rotation = targetRotation;
                }
              
                rigidbody.velocity = transform.forward * speed;
                anim.SetBool("Run", true);
            }
        }else{
      
        }
    }
2

Got it, just moved it into the FixedUpdate like this:

    void FixedUpdate(){
        if(anim.GetBool("Run")){
            rigidbody.velocity = transform.forward * speed;
        }
    }