if your dependency is a nuget package you can add a dependency tag in your nuspec file
<dependencies>
      <group targetFramework=".NETCoreApp3.0" >
         <dependency id="myproject.Interfaces" version="3.0.1" />
         <dependency id="myproject.Models" version="3.0.1" />
      </group>
      <group targetFramework=".NETCoreApp3.1" >
         <dependency id="myproject.Interfaces" version="3.0.1" />
         <dependency id="myproject.Models" version="3.0.1" />
      </group>
    </dependencies>
but if your dependency is a dll you can add as a normal file
<files>
 <file src="lib\netcoreapp3.0\myproject.Interfaces.dll" target="lib\netcoreapp3.0\myproject.Interfaces.dll" />
 <file src="lib\netcoreapp3.0\myproject.Models.dll" target="lib\netcoreapp3.0\myproject.Models.dll" />
   
 <file src="lib\netcoreapp3.1\myproject.Interfaces.dll" target="lib\netcoreapp3.1\myproject.Interfaces.dll" />
 <file src="lib\netcoreapp3.1\myproject.Models.dll" target="lib\netcoreapp3.1\myproject.Models.dll" />
</files>