portable application settings

App.cs

public partial class App : YourApp
{
    private static SettingsManager Manager = new SettingsManager("./settings.json");
    public static Settings Settings { get { return Manager.Settings; } }
    ...
}

Settings.cs

namespace MyApp.Configuration;

using System;
using System.Collections.Generic;
using System.Text;
using CommunityToolkit.Mvvm.ComponentModel;

public partial class Settings : ObservableObject
{
    public Settings() : base()
    {
    }

    [ObservableProperty]
    private Uri source = new Uri("https://gist.github.com/");

    [ObservableProperty]
    private bool shouldDoThis = false;
    
    [ObservableProperty]
    private bool shouldDoThat = true;

    [ObservableProperty]
    private int timeToWait = 3600;
}

SettingsManager.cs

namespace MyApp.Configuration;

using System;
using System.IO;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

public class SettingsManager
{
    private Settings settings = new Settings();
    public Settings Settings { get => settings; set => settings = value; }
    public string FileName;

    public SettingsManager(string fileName)
    {
        FileName = fileName ?? throw new ArgumentNullException(nameof(fileName));
        Load();
        settings.PropertyChanged += OnSettingsChanged;
    }

    private void OnSettingsChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        Task.Run(SaveAsync).Wait();
    }

    private void CreateDirectory()
    {
        var dir = Path.GetDirectoryName(FileName);
        if (!Directory.Exists(dir))
        {
            Directory.CreateDirectory(dir);
        }
    }

    private void Load()
    {
        CreateDirectory();

        if (!File.Exists(FileName))
        {
            SaveAsync();
            return;
        }

        var jsonString = File.ReadAllText(FileName, Encoding.UTF8);
        var settings = JsonSerializer.Deserialize<Settings>(jsonString);
        this.Settings = settings;
    }

    private async Task SaveAsync()
    {
        CreateDirectory();
        using FileStream createStream = File.Create(FileName);
        await JsonSerializer.SerializeAsync(createStream, Settings);
        await createStream.DisposeAsync();
    }
}