MacBook M3 Pro + Dell UD22 – Only One Monitor Detected via USB-C + HDMI
 

Hi,

I have a MacBook M3 Pro and recently purchased the Dell Universal Dock UD22. Unfortunately, I'm unable to use two monitors at the same time when connecting them via USB-C and HDMI.

Here’s what happens: when I connect two monitors—one via USB-C and one via HDMI—they both display the exact same image, and macOS only detects one external display. However, if I connect them individually, everything works fine.

I've also tested this both with and without the DisplayLink software installed, and the behavior is exactly the same.

My question is:
Is this expected behavior? Is it not possible to use USB-C and HDMI outputs simultaneously for extended displays on the UD22 when using a MacBook, and should I be using DisplayPort instead?

Thanks in advance for your help!

The UD22 combines two different technologies internally in order to drive the connected displays. The USB-C video output and HDMI video output use a DisplayPort Multi-Stream Transport Hub (also known as DP MST) to drive the displays. macOS does not support DP MST, which is why your displays are mirrored.

The DisplayPort video outputs of the UD22 are driven by DisplayLink technology. Can you connect one of the two displays to one of the DisplayPort outputs within the dock?

Solution to the issue
 

I had the same problem, understood the dock used an incompatible bus, and solved it by buying a Pulgable USBC-6950M (Plugable USB C to HDMI Adapter, Dual Monitor 4K 60Hz for Apple Mac M1/M2/M3, DisplayLink Multiple Displays for Thunderbolt MacBook or iMac) from Amazon.

My displays work fine now, but the DisplayLink software is still really buggy and gives unexpected behaviour. Downgrading drivers has helped.