ASP.Net Core 3.0 Preview 3 adds support for creating worker services, which are background services like Windows services and Linux daemons. There is a new template for creating a worker service in Visual Studio as well.
To work with worker services in Visual Studio, you should have the beta versions (Preview Version 3 or later) of ASP.Net Core 3.0 and .Net Core 3.0 runtimes installed on your system.