Multiplus II GX missing ve.can ports?

It either requires unsupported mods being loaded, or is a device intended for Pi use. Also unsupported.
Not everyone is ready to go unsupported, and mods have been a huge source of instability recently.
If the OP wants a fully supported and tested solution, the best option for an old integrated Multi GX is to upgrade to an external Cerbo GX or similar.
If they are happy to fiddle with third party devices and understand the consequences, then indeed, little to lose, apart from using up the only USB port.
Just remember that because it works today, does not mean it will work tomorrow as the software stack continues to evolve.