var modalCommands = _client.UseModalCommands(new ModalCommandsConfiguration()
{
    Services = _sp
});
modalCommands.RegisterModals(Assembly.GetExecutingAssembly());

var modal = ModalBuilder.Create("food")
    .WithTitle("Super cool modal!")
    .AddComponents(new TextInputComponent("Favorite food", "fav-food", "Pizza, Icecream, etc", max_length: 30))
    .AddComponents(new TextInputComponent("Why?", "why-fav", "Because it tastes good", required: false, style: TextInputStyle.Paragraph));

public class FoodModal : ModalCommandModule
{
    [ModalCommand("food")]
    public async Task GetFavFoodAsync(ModalContext ctx, string food, string reason)
    {
        await ctx.Interaction.CreateResponseAsync(InteractionResponseType.ChannelMessageWithSource,
            new DiscordInteractionResponseBuilder().WithContent($"Your favorite food is: {food}. Reason: {reason}").AsEphemeral());
    }
}

    public class IntConverter : IModalArgumentConverter<int>
    {
        // This method will convert the string to an int.
        public Task<Optional<int>> ConvertAsync(string value, ModalContext ctx)
        {
            return Task.FromResult(int.TryParse(value, out var res) ? Optional.FromValue(res) : Optional.FromNoValue<int>());
        }

        // This method will convert the int to a string.
        public string ConvertToString(int value) => value.ToString();
    }

buttonCommands.RegisterConverter(new ShortConverter());