[pax]

Так всего лишь надо повернуть вектора джойстика с учетом камеры.

//Примерно так
            Vector2 JoystickPosition = _Joystick.GetComponent<EasyJoystick>().JoystickTouch;
            if (JoystickPosition.magnitude != 0)
            {
                Destination.x = JoystickPosition.x;
                Destination.z = JoystickPosition.y;
                Destination.y = 0;
                var cameraForward = Camra.main.transfrom.forward;
                cameraForward.y=0;
                cameraForward.Normalize();
                var rotation = Quaternion.LookRotation(cameraForward);
                Destination = rotation * Destination;

                _Sphere.rigidbody.AddForce(Destination * Time.deltaTime * ForceMultiplier);
                Debug.Log(Rotation);
            }