Cable between iPad and iMac

I use the Duet app to extend the screen of my iMac (Retina 5K, 27 inch, Late 2014) which has old thunderbolt ports and my iPad pro which has a USB C port.

I use the app with wifi, so without a cable, but it’s jerky and not pleasant to work with. So I would like to connect my 2 machines with a cable but I don’t know which one….

An advice ? Or an idea to have something optimal?

Thank you and good day.