What you want is a Library Part, not an Add-On. (Add-ons add new program functionality to ArchiCAD.)
Always use the "Search" function here first ...
http://archicad-talk.graphisoft.com/viewtopic.php?p=4559&highlight=volkswagen#4559
Take a look here:
http://archicad-talk.graphisoft.com/viewtopic.php?t=2434
I couldn't find the Studio Arkada object just now ... someone?
Perhaps what you want can be purchased here (alfaville):
http://www.objectsonline.com/customer/search.php?substring=volkswagen
Almost any 3D object can be brought into ArchiCAD as a library part, too - dwg, 3ds, etc.
Google for: "volkswagen beetle" 3ds free model
Move the 3dsin add-on from your Goodies folder into your Add Ons folder, and then you can open the 3DS from the Extras menu, converting it to a GDL object. (Search the forums to find out more about doing this.)
Karl
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators