The main library is available as Telegram.Bots. It provides all the Types and Requests along with the HTTP and JSON support.
To add long polling, Telegram.Bots.Extensions.Polling can be used.
If you use the webhook approach and intend to respond to updates directly by returning the desired method data, you will need to integrate the serializer with your ASP.NET Core project and that can be done via Telegram.Bots.Extensions.AspNetCore.