How to Make a Settings Menu in Unity

using System.Collections.Generic;
using System.Linq;
using TMPro;
using UnityEngine;
using UnityEngine.Audio;

public class SettingsMenu : MonoBehaviour
{
    [SerializeField] private TMP_Dropdown _displayResolution;
    [SerializeField] private TMP_Dropdown _displayMode;
    [SerializeField] private AudioMixer _audioMixer;
    [SerializeField] private TMP_Text _soundLevel;

    private List<ScreenMode> _screenModes = new()
    {
        new ScreenMode("Full Screen", FullScreenMode.FullScreenWindow),
        new ScreenMode("Windowed", FullScreenMode.Windowed),
        new ScreenMode("Maximized Window", FullScreenMode.MaximizedWindow)
    };

    private void Start()
    {
        DisplayResolution();
        DisplayMode();
    }

    public void DisplayResolution()
    {
        List<Resolution> resolutions = Screen.resolutions.Reverse().ToList();

        foreach (Resolution resolution in resolutions)
        {
            TMP_Dropdown.OptionData option = new();
            option.text = resolution.ToString();

            _displayResolution.options.Add(option);
        }

        _displayResolution.value = resolutions.Count;
        _displayResolution.value = resolutions.FindIndex(x => x.ToString() == Screen.currentResolution.ToString());
    }

    public void DisplayMode()
    {
        foreach(ScreenMode screenMode in _screenModes)
        {
            TMP_Dropdown.OptionData option = new();
            option.text = screenMode.Name;

            _displayMode.options.Add(option);
        }

        _displayMode.value = _screenModes.Count;
        _displayMode.value = Screen.fullScreen ? 0 : 1;
    }

    public void Sound(float volume)
    {
        _audioMixer.SetFloat("Volume", volume);
        _soundLevel.text = $"{Mathf.Round(volume * 100)}%";
    }

    public void Quality(int index)
    {
        QualitySettings.SetQualityLevel(index);
    }

    public void SaveDisplayResolution()
    {
        List<Resolution> resolutions = Screen.resolutions.ToList();

        Resolution resolution = resolutions.Find(x => x.ToString() == _displayResolution.options[_displayResolution.value].text);
        Screen.SetResolution(resolution.width, resolution.height, Screen.fullScreenMode);
    }

    public void SaveDisplayMode()
    {
        FullScreenMode screenMode = _screenModes.Find(x => x.Name == _displayMode.options[_displayMode.value].text).FullScreenMode;
        Screen.SetResolution(Screen.width, Screen.height, screenMode);
    }
}

using UnityEngine;

public class ScreenMode
{
    private string _name;
    private FullScreenMode _fullScreenMode;

    public ScreenMode(string name, FullScreenMode fullScreenMode)
    {
        _name = name;
        _fullScreenMode = fullScreenMode;
    }

    public string Name => _name;
    public FullScreenMode FullScreenMode => _fullScreenMode;
}