Unable to connect MacBook Air M4 to ASUS portable monitor

Asus – ASUS MB168B Portable USB Monitor

This monitor connects to a computer via USB 2.0 or 3.0. Neither of those was designed to carry a video signal, and there's a line saying "The MB168B features ASUS EzLink technology that offloads graphics processing from the PC to dedicated hardware in the monitor."

I think that's a fancy way of saying that it relies on some workaround like DisplayLink that requires the installation of a special driver on the host computer. It doesn't make any use of your Mac's USB-C (DisplayPort) output.

Sure enough, in the product manual, page 2-2 tells you to go to the Asus site to download and install a driver. There are several drivers for macOS in the Support area; the most recent is for Big Sur, Monterey, and Ventura. Whether it will work on Sequoia is anyone's guess.

Another issue with this monitor may be power consumption. They claim that it can run in a bus-powered way off of a USB 3.0 port. USB 3.0 specifications require host ports to provide 4.5W (900 mA @ 5V) of power – which seems like an awfully small amount of power to operate a backlit 16" monitor.