Settings.cs

public static class Settings
{
    private static ApplicationDataContainer _settings = ApplicationData.Current.LocalSettings;

    public static bool IsFirstRun
    {
        get
        {
            if (_settings.Values.TryGetValue(nameof(IsFirstRun), out var isFirstRun))
            {
                return (bool)isFirstRun;
            }
            return true;
        }
        set => _settings.Values[nameof(IsFirstRun)] = value;
    }
}