Just a side note: This article is about a "Windows executable build from Unity". If you build directly for UWP in Unity, there is no extra work: just code on using the UWP APIs. Here are the details - https://docs.unity3d.com/Manual/windowsstore-scripts.html
Please note that, because the dll is using .NET 4.6, you will not able to run in Unity. Do not try play the app in Unity without compilation directives.