CountryService.cs

public async Task<List<Country>> LoadCountries()
{
    try
    {
        using var stream = await FileSystem.OpenAppPackageFileAsync("countries.json");
        using var reader = new StreamReader(stream);
        var contents = reader.ReadToEnd();
        var countries = JsonSerializer.Deserialize<List<Country>>(contents);
        return countries;
    }
    catch(Exception ex)
    {
        throw new Exception(ex.Message);
    }
}