Player keeps teleporting to a set Y coordinate when moving

Hello,

I am a complete beginner to Unity and its scripting, but I still tried to make a 3rd person player controlling system (with the help form a tutorial). Keep in mind it doesn't look like a game at all, it's just a blob moving across an empty space, but that's beside the point.

My problem is that when I press a key (w, a, s, or d) my player teleports upwards a little and then falls back down when I stop holding the key

Some extra info: The player has a character controller, rigidbody and a capsule collider (and a script of course). Here is the script assigned to the player.

If you have any additional questions, I'll try to answer them as soon as possible! Thanks!

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ThirdPersonMovement : MonoBehaviour
 {
     public CharacterController controller;
     public Transform cam;
     public float speed = 6f;
     public float turnSmoothTime = 0.1f;
     float turnSmoothVelocity;
 
   // Update is called once per frame
     void Update()
     {
         float horizontal = Input.GetAxisRaw("Horizontal");
         float vertical = Input.GetAxisRaw("Vertical");
         Vector3 direction = new Vector3(horizontal, 0f, vertical).normalized;
 
         if (direction.magnitude >= 1f)
         {
             float targetAngle = Mathf.Atan2(direction.x, direction.z) * Mathf.Rad2Deg + cam.eulerAngles.y;
             float angle = Mathf.SmoothDampAngle(transform.eulerAngles.y, targetAngle, ref turnSmoothVelocity, turnSmoothTime);
             transform.rotation = Quaternion.Euler(0f, angle, 0f);
 
             Vector3 moveDir = Quaternion.Euler(0f, targetAngle, 0f) * Vector3.forward;
             controller.Move(moveDir.normalized * speed * Time.deltaTime);
         }
     }
 }