Unity is slightly laggy in the game in the editor but even more laggy in the built version.

Unity is laggy when using the game preview in the editor. There's a stutter that is hard to explain. The framerate is high but there is still this weird stutter. It is even worse when I build the game and play it from there. I looked online and tried to turn off vsync as well as change the graphic settings, but nothing seems to be fixing it. I used Brackey's first person controller tutorial to make my first person controller.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerMovement : MonoBehaviour
 {
     public CharacterController controller;
 
     public GameObject character;
     public GameObject gun;
 
     public Camera player;
 
     public ParticleSystem wind;
 
     public static float speed = 8f;
     public float gravity = -9.81f;
     public float jumpHeight = 3f;
 
     public KeyCode sprint;
     public KeyCode crouch;
 
     public Transform groundCheck;
     public float groundDistance = 0.4f;
     public LayerMask groundMask;
 
     Vector3 velocity;
     bool isGrounded;
 
     // Start is called before the first frame update
     void Start()
     {
 
     }
 
     // Update is called once per frame
     void FixedUpdate()
     {
 
         /*if (Input.GetKeyDown(sprint))
         {
             speed = 12;
             player.fieldOfView = 68;
             wind.Play();
             wind.enableEmission = true;
         }
         else if (Input.GetKeyUp(sprint))
         {
             speed = 8;
             player.fieldOfView = 60;
             wind.enableEmission = false;
             wind.Stop();
         }*/
 
         isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);
 
         if(isGrounded && velocity.y < 0)
         {
             velocity.y = -2f;
         }
 
         float x = Input.GetAxis("Horizontal");
         float z = Input.GetAxis("Vertical");
 
         Vector3 move = transform.right * x + transform.forward * z;
 
         controller.Move(move * speed * Time.deltaTime);
 
         if(Input.GetButtonDown("Jump") && isGrounded)
         {
             velocity.y = Mathf.Sqrt(jumpHeight * -2f * gravity);
         }
 
         velocity.y += gravity * Time.deltaTime;
 
         controller.Move(velocity * Time.deltaTime);
 
         /*if (Input.GetKeyDown(crouch))
         {
             speed = 6;
             character.transform.localScale = new Vector3(1, .4f, 1);
             gun.transform.localScale = new Vector3(.40686f, 1, .40686f);
         }
         else if (Input.GetKeyUp(crouch))
         {
             speed = 8;
             character.transform.localScale = new Vector3(1, 1, 1);
             gun.transform.localScale = new Vector3(.40686f, .40686f, .40686f);
         }*/
     }
 }
 
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class MouseLook : MonoBehaviour
 {
     public float mouseSensitivity = 100f;
 
     public Transform playerBody;
 
     private float xRotation = 0f;
 
     // Start is called before the first frame update
     void Start()
     {
         
         Cursor.visible = false;
         Cursor.lockState = CursorLockMode.Locked;
     }
 
     // Update is called once per frame
     void FixedUpdate()
     {
         float mouseX = Input.GetAxis("Mouse X") * mouseSensitivity * Time.deltaTime;
         float mouseY = Input.GetAxis("Mouse Y") * mouseSensitivity * Time.deltaTime;
 
         xRotation -= mouseY;
         xRotation = Mathf.Clamp(xRotation, -90f, 90f);
 
         transform.localRotation = Quaternion.Euler(xRotation, 0f, 0f);
         playerBody.Rotate(Vector3.up * mouseX);
     }
 }