Why won't my MacBook Pro M4 detect Two Monitors?

jukkathefinnishflash wrote:

I have connected 2 external monitors to my MacBook Pro M4 with Unisynk 9-port dock through HDMI. The dock is attached to computer with USB-C. MacBook won’t detect monitors as 2 separate ones but as 1 together. Is there any other way to get MacBook understand that those are individual monitors than attaching the other one directly to MacBook?

Is that "Unisynk 9-port dock" a Thunderbolt dock?

My bet is that it isn't – and that is the problem. Macs only support connecting two displays to a single dock, in a hardware-supported way, when

• The Mac in question can drive at least two external monitors over USB-C or Thunderbolt, and
• The dock is a Thunderbolt dock (not a plain USB-C (USB, DisplayPort Alt Mode) one

Thunderbolt provides an extra-wide "data highway" and the Mac wants to see that extra-wide highway before it's willing to provide two video signals – even if the two monitors in question are low-resolution ones.

Here's what I found on the Unksynk site:

Unisynk – 9 Port Dual Display USB-C Docking Station

Under Compatibility it says,

"Designed to use mainly with PC laptops. Make sure the USB-C port on your device supports DisplayPort protocol for video. Supports PowerDelivery protocol. Support for HDR, DSC, HDCP 2.3, MAC pass-through and PxE-Boot. Works with Macbook but only duplicates the screen when using both HDMI."

My guess is that this dock uses the equivalent of DisplayPort MST daisy-chaining to drive the second HDMI output. Macs don't support that. The other possibility is that it uses a second-class workaround like DisplayLInk to do so – which would require the installation of a special driver and the compromises that come with that.

You need to plug one of your monitors directly into the MacBook – or to get a better dock.