when I jump up to an object that is a cube I reach the step offset and it jitters for a little bit before falling to the ground again. I can remove the step offset altogether but that's not what I want as my game is baste around parkour. when I was making this I was following a Brackeys tutorial on YouTube. Brackeys tutorial. can anyone help me out? ,first person object , the object causing most problems, objects in scene

using System.collections;
using System.Collections.Generic;
using UnityEngine;

public class keymovement : MonoBehaviour
{
public CharacterController controller;


public float speed = 12f;
public float gravity = -10f;

public Transform groundcheck;
public float groundDistance = 0.5f;
public LayerMask groundMask;

public float jumpheight = 3f;

Vector3 velocity; 
bool isgrounded;


void Update()
{
    isgrounded = Physics.CheckSphere(groundcheck.position, groundDistance, groundMask);

   

    if (isgrounded && velocity.y < 0)

    {
        velocity.y = -2;
  }

    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.GetButton("jump") && isgrounded)
    {
        velocity.y = Mathf.Sqrt(jumpheight * -2f * gravity);
    }

    velocity.y += gravity * Time.deltaTime;

    controller.Move(velocity * Time.deltaTime);
    }

      
    }
    }
    }