>C:\Program Files\dotnet\sdk\3.0.100-preview6-012085\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Sdk.TargetingPackResolution.targets(194,5): error NETSDK1073: The FrameworkReference 'NETStandard.Library' was not recognized
<TargetFramework>netcoreapp3.0</TargetFramework>
<ItemGroup>
<PackageReference Include="System.Text.Encoding.CodePages" Version="4.6.0-preview5.19224.8" /> <!--It doesn't matter what's referenced-->
</ItemGroup>
Workaround here - https://github.com/dotnet/cli/issues/11378#issuecomment-499988244
Thank you for the link @JamesNK
Closing since this is an SDK issue that is fixed in latest SDK.
Updated to 16.4 and got this mess. Microsoft is losing its eye on the ball....