I can't change my game from fullscreen to windowed.

I have this script and when I build a game everything is working but not the fullscreen toggle. Thanks in Advance :D

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.Audio;
 using UnityEngine.UI;
 using TMPro;
 
  
 public class OptionsMenu : MonoBehaviour
 {
 
     public TMP_Dropdown resolutionDropdown;
     public AudioMixer Mixer;
     Resolution[] resolutions;
 
     void Start()
     {
 
         resolutions = Screen.resolutions;
         resolutionDropdown.ClearOptions();
         List<string> options = new List<string>();
 
         int CurrentResolutionIndex = 0;
         for (int i = 0; i < resolutions.Length; i++)
         {
             string option = resolutions[i].width + "X" + resolutions[i].height;
             options.Add(option);
             if (resolutions[i].width == Screen.currentResolution.width && resolutions[i].height == Screen.currentResolution.height)
             {
                 CurrentResolutionIndex = i;
             }
         }
         resolutionDropdown.AddOptions(options);
         resolutionDropdown.value = CurrentResolutionIndex;
         resolutionDropdown.RefreshShownValue();
     }
     public void SetResolution(int resolutionIndex)
     {
         Resolution resolution = resolutions[resolutionIndex];
         Screen.SetResolution(resolution.width, resolution.height, Screen.fullScreen);
     }
 
     public void SetVolume(float volume)
     {
         Mixer.SetFloat("volume", volume);
     }
     public void Quality(int QualityIndex)
     {
         QualitySettings.SetQualityLevel(QualityIndex);
     }
     public void SetFullscreen(bool IsFullScreen)
     {
         Screen.fullScreen = IsFullScreen;
     }
 }