IBM Model M keyboard not recognised on Mac

Hello, I have this IBM Model M keyboard made 1993 and it's not recognising on my Mac. The keyboard uses the ps2 connector so I bought an adaptor to USB. This keyboard and adaptor system works fine on two Windows PC running win10 and one running XP. But it just won't work with my 2010 iMac running Sierra and another 2015 iMac running El Capitan. I have tried to turn off bluetooth and use keyboard setup assistance but it won't work.

Anyone have any suggestions?? Maybe some drivers to download somewhere?

Thanks