You can see, when choose "ASP.NET Web API", no namespace listed out for it, the navigate URL is https://learn.microsoft.com/en-us/dotnet/api/?view=aspnet-webapi-5.2 ...

This library simplifies setting up an ASP.NET Core application to use the GOV.UK Design System. It includes tag helpers to produce GDS components which integrate with ASP.NET Core's model binding ...