This article explains the use of an Elo touchscreen with an Apple iOS product

Apple iOS does not currently support external touch devices on their hardware. Elo monitors could be used as an external video display, providing the proper USB-C/Lightning to HDMI adapter is used; however, all touch interactions would have to occur on the Apple device's screen and touch would not work on the Elo screen.

Elo Touchscreens require USB HID protocol for touch, Apple iOS does not support this.

See discussion on Apple's forum HERE

See related article below:
Apple TV Compatibility with Elo Monitors