1

Here is my code (not mine, tho)

private void Awake()
{
    lineRenderer = GetComponent<LineRenderer>();
}
private void Update()
{
    castRay();
}
void castRay()
{
    ray = new Ray(transform.position, transform.up);

    lineRenderer.positionCount = 1;
    lineRenderer.SetPosition(0, transform.position);

    count += Time.deltaTime * lineDrawSpeed;
    
    for(int i = 0; i < reflect; i++)
    {
        Debug.DrawRay(ray.origin, ray.direction * count);
        if(Physics.Raycast(ray, out hit, count))
        {
            lineRenderer.positionCount += 1;
            lineRenderer.SetPosition(lineRenderer.positionCount - 1, hit.point);
            
            ray = new Ray(hit.point, Vector3.Reflect(ray.direction, hit.normal));
            print(hit.distance);
            if(hit.transform.tag !="Mirror")
            {
                break;
            }
        }
        else
        {
            lineRenderer.positionCount += 1;
            lineRenderer.SetPosition(lineRenderer.positionCount -1, ray.origin + ray.direction * count);
        }
    }
}

and video Raycast(test) - YouTube

2

Add a RigidBody2D to the object with the LineRenderer and the following code should move the line object as you wish, just without drawing the Ray:

[SerializeField] private int lineDrawSpeed;
private RigidBody2D rigidbody; //initialize in the Start()

void Update()
{
	transform.Translate(Vector3.right * Time.deltaTime * lineDrawSpeed);
}

void OnCollisionEnter2D(Collision2D collision)
{
    var reflectedPosition = Vector2.Reflect(transform.right, collision.contacts[0].normal);
    rigidbody.velocity = reflectedPosition.normalized * lineDrawSpeed;
    var direction = rigidbody.velocity;
    rigidbody.freezeRotation = false;
    rigidbody.MoveRotation(Mathf.Atan2(direction.y, direction.x) * Mathf.Rad2Deg);
    rigidbody.angularVelocity = 0f;
}

You should get a normalized reflected Vector (normalized vector has magnitude = 1). This will keep your desired length and speed. Then the easier way is to find the angle of rotation with the inverse (arcus) tangent of y/x from your normalized reflected vector.