NuGet Framework package with dependencies from Core project - visual-studio

Question

I am trying to reference from a .NET Core 3.1 project, a NuGet package that targets only net40 via the NuGet compatibility shim. The package is added to my project, however the net40 dependencies are not.
The package is structured as:
lib\
net40\
AssemblyA.dll
nuspec:
<dependencies>
<group targetFramework="net40">
<dependency id="PackageB" version="1.0" />
</group>
</dependencies>
Visual Studio's Package Manager lists the dependencies, but when installed, the dependencies are not listed by VS' Preview Changes window and are indeed not installed. PackageB also targets net40.
It does work if I:
Include the dependencies in an "Any" (blank) dependency group as well as under net40
Remove the net40 dependency group and list the package directly under <dependencies> as a flat list
Remove the net40 under lib\ and use a flat list
These are not ideal as it obfuscates the true nature of the targets frameworks. The last two produce NU5128 on pack. For future reference, I should mention that it's required to remove the dependencies from the local cache for even these scenarios to work (surely a bug?).
Any ideas on how to pull dependencies from such packages? Is this simply not supported? A good test example of this is the "Polly.Net40Async" package.
(VS: 16.6.5, dotnet: 3.1.302, PackageReference, Windows 10)

Answer 1

I am trying to reference from a .NET Core 3.1 project, a NuGet package
that targets only net40 via the NuGet compatibility shim. The package
is added to my project, however the net40 dependencies are not.
The nuget package only targets to net40 which means the package is used for net framework 4+.
And by default, Net Core projects cannot use this type of nuget unless the package and dependencies are listed as supporting Net Core or Net Standard.
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Also, you can notice the info from the Polly.Net40Async nuget package:
group targetFramework="net40" means that if your project targetframework version is 4+, it will install the listed dependencies.
So you should not install this type of packages into Net Core 3.1 project. And it is designed by the author.
Besides, if you change the sub folder of lib in the nuget package to any, you can add the dependencies into the Net Core project.
After all, any means it targets to any framework versions--net core, net standard, net framework. And you just need to remove the condition of the dependency (contention on Net Framework 4+).
====================================
Add more detailed info
Update 1
Actually, Net Core projects can install some nuget packages which only targets to Net Framework.
In my side, the package can be installed in the Net Core project.However, there is a warning which shows it may not be fully compatible with your Net Core project. Although you can use it, there are still some problems just not encountered in special situations.
For the dependencies, since your project targets to Net Core rather than Net Framework, the dependencies will not be installed automatically along with the main package. But you can manually install these dependencies separately through Nuget Package Manager UI.(search them and then install them one by one).
And if condition group targetFramework="net40" is met, it will install these dependencies automatically along with the main nuget package. But since your project targets to Net Core, it will not install them automatically.
As a suggestion, you could search these dependencies on the Nuget Package Manager UI, and then manually install them separately.