Fyi my Solution file has C# projects, .net V4.x and .net 8

The plugin relies on IntelliJ IDE providing information about "source code" files location. If the IntelliJ does not provide such information, then the plugin does not display any files. This happens, for projects where there is no source code at all. For example if you have a project with some text files or something like that.

There is a solution for that.

In the IntelliJ IDE in projects panel, right click on the folder you want to mark as source code folder, in the dropdown menu select "Mark directory As" and then select "Sources Root". Similarly you can use the same method to "Exclude" some directories.

I do not have experience with Rider and C# projects but I hope this helps. Please let me know if this helps. If not I will investigate it further to find solution that works.