Pause menu example in Unity (C#) - Stop using Unity!

PauseMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;
using System;

public class PauseMenu : MonoBehaviour
{
 public void MainMenu()
    {
        SceneManager.LoadScene(0);
    }

    public void Restart()
    {
       pauseMenu.SetActive(false);
       SceneManager.LoadScene(1);
       time = 0f;
       started = true; 
    }


    public GameObject pauseMenu;

    public void pause()
    {
        started = false;
        pauseMenu.SetActive(true);
    }

    public void resume()
    {
        pauseMenu.SetActive(false);
        started = true;
    }

    void Update()
    {
        if (started == true && Input.GetKeyDown(KeyCode.Escape))
        {
           pause();
        } else 

        if (started == false && Input.GetKeyDown(KeyCode.Escape))
        {
            resume();
        }
    }
 }