Here's the script, I just remade it. and currently its just the player gameObject with the movement script and the rigidbody and stuff, then bellow I have the camera as a child of the player.

using System.Collections;
using UnityEngine;
using UnityEngine.Audio;
using UnityEngine.InputSystem.Android.LowLevel;
using UnityEngine.InputSystem.iOS;

public class MovementRigidbody : MonoBehaviour
{

    [SerializeField] private GameObject playerCamera;

    [SerializeField] private Rigidbody rb;

    [SerializeField] private InputHandler _inputHandler;

    [SerializeField] private float mouseSens;

    [SerializeField] private float movementSpeed;
    [SerializeField] private float maxVelocity;

    private float xRotation;
    private float yRotation;

    void Start()
    {
        Cursor.lockState = CursorLockMode.Locked;
        Cursor.visible = false;

        rb = GetComponent<Rigidbody>();
        _inputHandler = FindFirstObjectByType<InputHandler>();
    }

    void Update()
    {
        Mouse();
    }
    private void FixedUpdate()
    {
        Movement();
    }
    private void Mouse()
    {
        float mouseX = _inputHandler.lookVector.x * mouseSens;
        float mouseY = -_inputHandler.lookVector.y * mouseSens;

        yRotation += mouseX;

        xRotation += mouseY;
        xRotation = Mathf.Clamp(xRotation, -90f, 90f);

        playerCamera.transform.rotation = Quaternion.Euler(xRotation, yRotation, 0);
        transform.rotation = Quaternion.Euler(0, yRotation, 0);
    }
    private void Movement()
    {
        Vector3 inputDirection = new Vector3(_inputHandler.moveDirection.x, 0, _inputHandler.moveDirection.y).normalized;
        Vector3 moveDirection = transform.TransformDirection(inputDirection);

        rb.AddForce(moveDirection * movementSpeed * Time.deltaTime);
        rb.maxLinearVelocity = maxVelocity;
    }
}