Hey OUTLAW,
I have such things bookmarked,
Confirmed Aftermarket Screens/Monitors that work with the Onefinity
The Monitor and the Touch are in fact two different things, even if they always are inside the same device. That’s why you need at least two different cables (besides the third, power cable) and why they have different connectors. The Monitor you need is any HDMI (or DVI-D or DVI-I which is compatible to HDMI) monitor. You connect it to the HDMI output of the Onefinity Controller which contains a Raspberry Pi 3B. And for the Touch it is the same, you have to use one that works on a Raspberry Pi 3, but the touch device is an input device, therefore you need a second cable with which you connect the monitor to a USB Port of the Onefinity Controller.
How to connect the Touch Display is described in the Onefinity Manual on page 38 and 39.
The monitor you need is in fact a monitor with a Touch device that the OS has a driver for. The operating system of the Onefinity Controller is Raspberry Pi OS (formerly Raspbian because it is based on Debian GNU/Linux), so in fact what you have to look for, is a Touch Monitor that works on a Raspberry Pi 3B and under Raspberry Pi OS. Note that the version of the Raspberry Pi OS on the Onefinity Controller version 1.0.9 is Raspberry Pi OS 9.3 Stretch of 2017 with a Linux kernel 4.9. But don’t worry, Linux has integrated driver support for many touch devices. Usually you don’t need to install drivers separately. Which touch monitors are running successfully on the Onefinity Controller is reported here.
Note that you don’t forcibly need a Touch Monitor to use the Onefinity CNC. You can use a a (non-touch) monitor, a mouse and a keyboard. The desire to use a Touchscreen on a CNC milling machine comes from the fact that when milling wood, there could be wood dust around, and most keyboards and mice don’t really like that.