Microsoft.Extensions.Hosting.WindowsServices contains implementation for using hosting in Windows Services.
Documentation can be found at https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.hosting.
The APIs and functionality are mature, but do get extended occasionally.
Microsoft.Extensions.Hosting.WindowsServices is included in the ASP.NET Core shared framework. The package is deployed as out-of-band (OOB) too and can be referenced into projects directly.