You cannot create a traditional Windows Service using the UWP platform. However, you can create a an App Service that uses a Background Task. You can communicate between an app and your UWP App Service using a defined API surface much like a web service. I've included links below with more information.
Create and consume an app service
https://learn.microsoft.com/en-us/windows/uwp/launch-resume/how-to-create-and-consume-an-app-service
Hi, does the following answer make sense? Do you have other questions?