Visual Studio won't accept UWP version for Nugget package?

This is driving me nuts!

I'm trying to install Microsoft.Build. Using Nugget Manager I can successfully install Microsoft.Build.Framework but not Microsoft.Build. I've upgraded to the latest version 1903 (build 18362), but still get the error:

Severity Code Description Project File Line Suppression StateError NU1202 Package Microsoft.Build 16.5.0 is not compatible with uap10.0.18362 (UAP,Version=v10.0.18362) / win10-x64. Package Microsoft.Build 16.5.0 supports: - net472 (.NETFramework,Version=v4.7.2) - netcoreapp2.1 (.NETCoreApp,Version=v2.1)

But the framework requirements for both are the same? Anyone seen this or have some idea what the problem is?

thanks