Please check you don’t have some files from WIP installers.
Now RiR installs in %ProgramData%\Autodesk\Revit\Addins
.
Go to %APPDATA%\Autodesk\Revit\Addins\2021
and remove RhinoInside.Revit.addin and RhinoInside.Revit folder.
Same applies to other Revit versions.