Keeping this up to date, I installed the Import addon today and unlike earlier versions it works without additional libraries, right off.
Installed on Blender 2.90 for Windows (10 X64).
I installed addon version 0.0.8, downloaded from Github, which works well.
Edit: there is no preinstalled version, the earlier version in my case, must have originated from an earlier attempt to install the Rhino Importer addon then within Blender 2.8x, that carried through to newer Blender installations.
The addon version packaged with 2.90 is 0.0.6, which did not work, did not run at all, only a screen of errors.
I removed it and installed addon version 0.0.8, downloaded from Github, which works well.
(Note that the geometry from Rhino is not how one would model in Blender, faces of one mesh are usually not linked, only coplanar ones are, lots of triangles, etc. It is what it is, the importer works)