I've see the X-TOUCH and I wish to know if I can use it with my XAIR18 or, sometime, with my Cubase Elements 10.5
I'd highly recommend you ask your Cubase question over on the Steinberg forum. Since you specifically said "Elements" I'd confirm that edition supports a Mackie control surface. With some DAWs, editions less than the "Pro" edition sometimes have less hardware support. In this case it may only be the LE or "Lite Edition" that is limited.