Can't archive my android project, "this package may not be fully compatible"

Whenever I try to archive my android project into an APK, I get this warning which prevents me from archiving:

Package 'Plugin.MediaManager 0.4.51' was restored using '.NETFramework version=v4.6.1' instead of the project target framework '.NETStandard,Version=v2.01. This package may not be fully compatible with your project.

The project builds just fine. Any ideas? The plugin I'm using 'Plugin.MediaManager' is essential and I need it in my project.

Thanks