Loading platform specific DLLs from "runtimes" folder in .NET 6

I have modular a windows app (exe). App has almost no references to nugets. In other project I have nugget reference to 'System.DirectoryServices'. App loads my other project (module) dynamically without reference to it (in csproj).

When I try to call something from 'System.DirectoryServices', I get 'PlatformNotSupportedException', because only placeholder DLL is loaded and platform specific DLL from runtimes folder is not loaded even if the files are there. When I add nuget reference to the app, everything works fine, but I don't want to lose modularity that way.

Can you guys please explain it to me, what is wrong? How can I tell the app to "look for" DLLs in runtimes folder even without nuget added to the app and without?