ResolutionChanger

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

public class ResolutionChanger : MonoBehaviour
{
    public TMP_Dropdown resolutionDropdown;

    private Resolution[] resolutions;

    void Start()
    {
        // Get all available screen resolutions
        resolutions = Screen.resolutions;

        // Clearing the current list in dropdown
        resolutionDropdown.ClearOptions();

        // Creating a list of strings for permissions
        List<string> options = new List<string>();

        int currentResolutionIndex = 0;

        for (int i = 0; i < resolutions.Length; i++)
        {
            // Correct access to Resolution properties
            string option = resolutions[i].width + " x " + resolutions[i].height;
            options.Add(option);

            // Check resolution
            if (resolutions[i].width == Screen.currentResolution.width &&
                resolutions[i].height == Screen.currentResolution.height)
            {
                currentResolutionIndex = i;
            }
        }

        // v
        resolutionDropdown.AddOptions(options);

        // Set the current resolution as selected in dropdown
        resolutionDropdown.value = currentResolutionIndex;
        resolutionDropdown.RefreshShownValue();
    }

    public void SetResolution(int resolutionIndex)
    {
        Resolution resolution = resolutions[resolutionIndex];
        Screen.SetResolution(resolution.width, resolution.height, Screen.fullScreen);
    }
}