How a .NET project add a C++/CLI library from NuGet?

Question

My project structure is: The main project is .NET framework 4.8, and the library develops by C++/CLI. I can add the file reference directly, it can work now.

For some reason, we don't want to reference the file, so we want to use NuGet to get the library.

I have published the package to our private NuGet feed, but when I install the package from NuGet, it shows the error:

Could not install package 'MyLib 1.0.3'. You are trying to install this package into a project that targets '.NETFramework, Version=v4.8', but the package does not contain any assembly references or content files that are compatible with that framework. For more information, contact the package author.

PS: I have set the ".NET Framework Target Version" to "v4.8".

This is my .nuspec file:

<?xml version="1.0"?>
<package >
  <metadata>
    <id>MyLib</id>
    <version>1.0.3</version>
    <authors>MyCompany</authors>
    <owners>MyCompany</owners>
    <requireLicenseAcceptance>false</requireLicenseAcceptance>
    <description>lib for Windows</description>
    <releaseNotes>This is the test publish.</releaseNotes>
    <copyright>Copyright 2019</copyright>
    <tags>lib native</tags>
  </metadata>
</package>

And it just contains one file:

\build
    \net48
        \MyLib.dll