Cannot deserialize JSON to new instances of type 'X'

I'm making a menu of options, and I want the settings made to be saved in .json format, that does not give any errors, but when I start the game and I want to load them, it says:

Can not deserialize JSON to new instances of type 'X'

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System.IO;
 
 public class SettingManager : MonoBehaviour {
     public Toggle fullscreenToggle;
     public Dropdown resolutionDropdown;
     public Dropdown textureQualityDropdown;
     public Dropdown antialiasingDropdown;
     public Dropdown vSyncDropdown;
     public Slider musicVolumeSlider;
     public Button applyButton;
 
     public AudioSource musicSource;
     public Resolution[] resolutions;
     public GameSettings gameSettings;
 
     void OnEnable()
     {
         gameSettings = new GameSettings();
 
         fullscreenToggle.onValueChanged.AddListener(delegate { OnFullscreenToggle(); });
         resolutionDropdown.onValueChanged.AddListener(delegate { OnResolutionChange(); });
         textureQualityDropdown.onValueChanged.AddListener(delegate { OnTextureQualityChange(); });
         antialiasingDropdown.onValueChanged.AddListener(delegate { OnAntialiaingChange(); });
         vSyncDropdown.onValueChanged.AddListener(delegate { OnVSyncChange(); });
         musicVolumeSlider.onValueChanged.AddListener(delegate { OnMusicVolumeChange(); });
         applyButton.onClick.AddListener (delegate { OnApplyButtonClick(); });
 
         resolutions = Screen.resolutions;
         foreach(Resolution resolution in resolutions)
         {
             resolutionDropdown.options.Add(new Dropdown.OptionData(resolution.ToString()));
         }
             
         if (File.Exists(Application.persistentDataPath + "/gamesettings.json") == true)
         {
             LoadSettings();
         }
     }
 
     public void OnFullscreenToggle()
     {
         gameSettings.fullscreen = Screen.fullScreen = fullscreenToggle.isOn;
     }
 
     public void OnResolutionChange()
     {
         Screen.SetResolution(resolutions[resolutionDropdown.value].width, resolutions[resolutionDropdown.value].height, Screen.fullScreen);
     }
 
     public void OnTextureQualityChange()
     {
         QualitySettings.masterTextureLimit = gameSettings.textureQuality = textureQualityDropdown.value;
     }
 
     public void OnAntialiaingChange()
     {
         QualitySettings.antiAliasing = gameSettings.antialiasing = (int)Mathf.Pow(2f, antialiasingDropdown.value);
     }
 
     public void OnVSyncChange()
     {
         QualitySettings.vSyncCount = gameSettings.vSync = vSyncDropdown.value;
     }
 
     public void OnMusicVolumeChange()
     {
         musicSource.volume = gameSettings.musicVolume = musicVolumeSlider.value;
     }
 
     public void OnApplyButtonClick()
     {
         SaveSettings();
     }
 
     public void SaveSettings()
     {
         string jsonData = JsonUtility.ToJson(gameSettings, true);
         File.WriteAllText(Application.persistentDataPath + "/gamesettings.json", jsonData);
     }
 
     public void LoadSettings()
     {
         gameSettings = JsonUtility.FromJson<GameSettings>(File.ReadAllText(Application.persistentDataPath + "/gamesettings.json"));
 
         musicVolumeSlider.value = gameSettings.musicVolume;
         antialiasingDropdown.value = gameSettings.antialiasing;
         vSyncDropdown.value = gameSettings.vSync;
         textureQualityDropdown.value = gameSettings.textureQuality;
         resolutionDropdown.value = gameSettings.resolutionIndex;
         fullscreenToggle.isOn = gameSettings.fullscreen;
     }
 }