MoveRotation stops working while player is moving

I started learning Unity not so long ago, and I wrote this third person camera controller script which works perfectly until I start moving the "player". The player in this case is just a simple cube with basic movements. This is my camera controls script:

 using UnityEngine;
 
 public class TargetedCameraController : MonoBehaviour
 {
     public GameObject target;
     public Vector3 offset;
     public float rotationSpeed;
     public float movementSmoothness;
     public float maxYRotation;
     public float minYRotation;
     public float maxCameraDistance;
     public float zoomSmoothness;
     public float cameraClippingMargin;
     GameObject helper;
 
     private void Start()
     {
         helper = gameObject.GetComponentInParent<Rigidbody>().gameObject;
         allowPlayerInput = true;
     }
 
     private void Update()
     {
         PlayerInput();
         CastRay();
         CameraRotation();
     }
     private void FixedUpdate()
     {
         FollowTarget();
     }
 
     //PLAYER INPUT MANAGER
     [HideInInspector] bool allowPlayerInput;
     private float inputX;
     private float inputY;
     int PlayerInput()
     {
         if (allowPlayerInput)
         {
             inputX = Input.GetAxis("Mouse X");
             inputY = Input.GetAxis("Mouse Y");
         }
         else
         {
             inputX = 0;
             inputY = 0;
         }
         return 0;
     }
 
     //CAMERA ROTAION MANAGER
     float rotY;
     float rotX;
     int CameraRotation()
     {
         //Calculate Vertical Rotation
         rotY -= inputY * rotationSpeed;
         rotY = Mathf.Clamp(rotY, minYRotation, maxYRotation);
 
         //Calculate Horizontal Rotation
         rotX += inputX * rotationSpeed;
         if(rotX >= 360)
         {
             rotX = 0;
         }
         if(rotX <= -360)
         {
             rotX = 0;
         }
 
         //Set Rotation
         helper.GetComponent<Rigidbody>().MoveRotation(Quaternion.Euler(rotY, rotX, 0));
         return 0;
     }
 
     //CAMERA MOVEMENT MANAGER
     Vector3 smoothPos;
     Vector3 offsetPos;
     int FollowTarget()
     {
         //Sets desired camera position, smooths follow and adds the custom offset
         offsetPos = target.transform.forward * offset.z + target.transform.right * offset.x + target.transform.up * offset.y;
         smoothPos = Vector3.Slerp(target.transform.position + offsetPos, helper.transform.position, movementSmoothness);
         helper.transform.position = smoothPos;
 
         //Set camera position
         transform.position = helper.transform.position + helper.transform.forward * -hitDistance;
         return 0;
     }
 
     //CAMERA PHYSICS MANAGER
     private Ray cameraDistanceRay;
     private float hitDistance;
     int CastRay()
     {
         //Cast the ray
         cameraDistanceRay = new Ray(helper.transform.position, transform.forward * (-hitDistance - cameraClippingMargin));
 
         //Get hit distance
         RaycastHit hit;
         if(Physics.Raycast(cameraDistanceRay, out hit) && hit.distance < hitDistance + 1 && hit.point != null)
         {
             hitDistance = Mathf.Clamp(hit.distance, 0.5f, maxCameraDistance);
             hitDistance = hitDistance - cameraClippingMargin;
         }
         else if (hitDistance != maxCameraDistance)
         {
             hitDistance = Mathf.Lerp(hitDistance, maxCameraDistance, zoomSmoothness);
         }
         return 0;
     }
 }

The "helper" is an empty object that I use to rotate and move the camera. The camera is moved away from the helper using the maxCameraDistance value and the Raycast hit distance. After some debugging I found that this is the line of code that gives me this problem:

 helper.GetComponent<Rigidbody>().MoveRotation(Quaternion.Euler(rotY, rotX, 0));

because when I try to change it to something, it doesn't stop working when the cube is moving (but then I cant make a limit for Y rotation so I really want to use this)

Here's a gif of what's going on: https://gyazo.com/35d6e35e8f4fe013b4b67bcad8ef4fea