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

That supports up to two external displays, But NOT over ONE USB-C cable out of the Mac.

in order to support up to TWO unique displays on ONE cable out of a Mac, the PORT, the cable, and the first device (Dock or Display) must all be genuine ThunderBolt.

this would work with a ThunderBolt Dock. But USB-C cables have only half as many data pathways, and can't support two modern displays on a Mac.

i was told by support this is a known issue, two monitors don't seem to work correctly (have M4 pro with pro chip). I tried TB5/TB4/HDMI adapater/DP cable all rated for 4k/240hz, but only one monitor would pick up at a time, even at 1080p 60hz and lid closed. they said expect an update but not sure when...speak to support and get your case added to the larger case so they can get this expedited and fixed - its' annoying as **** and i've spend a few hundred testing on TB4/TB5 docks from OWC and various 'will work' cables from Amazon. My M1 pro chip works perfect at 100hz to both monitors *Asus PG32UCDM*.

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.

I would suggest that you get a Thunderbolt hub or dock. Three vendors who have supplied Thunderbolt products for Mac users for a long time – and who have a wide selection of Thunderbolt gear – are

• Other World Computing
• SonnetTech
• CalDigit

Look for a Thunderbolt dock or hub that supports connection of two displays – but be wary of any that promise to support more than that.

The same for me.

I cannot use two extended monitors for now. It's happened after 22 March 2025. But I have used them for a year.

All hardware was the same, no changes.

I can use Monito wire thunderbold or using HDMI (only one, not both)

My setup:

Macbook 14 M3 PRO

macOS 15.3.2

Monotor 1: LG 27UL650-W

Monotor 2: LG 27UL650-W

Doc station: HP doc G5

Connection:

1. Monotor 1 => Doc station =>(ThunderBolt) Macbook
2. Monotor 1 =>(HDMI) Macbook

HowardMosk--

NEW discussion:

To get the attention you deserve, PLEASE start a NEW discussion.

If you did not immediately find your solution by reading through the existing postings, you likely do not have "exactly the same problem" and need to explain from the beginning. This discussion is already way too crowded with different problems posted by different users with different hardware, different versions of MacOS, and different displays.

Starting a new discussion will allow Readers to think hard about your exact situation and address the exact circumstances you are facing.

https://discussions.apple.com/post/question

what processor on your MacBook Pro?

{ULTRA MAX PRO [plain] } ??

I am really sorry you got an Apple support representative who was badly trained and does not have a deep undertaking of display issues. They misled you, badly. The correct information has been posted above.

There have been some issue with M4 and portable, Bus-powered displays, but they simply DO NOT APPLY to your situation. If you wait for a software update to correct something that has been so badly mis-diagnosed by Apple support, you will wait a VERY long time.

Your Mac supports these two displays on individual cables, RIGHT?

That tells you the issues are all with using the Docks you are using.

And if you were listening intently, readers told you can't run TWO displays on a USB-C Dock. a genuine ThunderBolt Dock is required.

I cannot run two monitors external period. I have tried TB5 cables direct to MBP, TB4 cables direct to MBP, TB5 cables to a TB5 dock, TB4 cables to a TB4 dock. USB-C to DP cables, USB-C to HDMI adapters, nothing works. My monitors are PG32UCDM, I set both to 100Hz 1440P and only one will display. I pull the cables the other displays. They both display on my M1 at 1440P 100hz. They don’t even work at 1080P/60hz together, lid is always closed. Please provide the case number you are referring too. I am aware of the issue you mentioned, it is not the same as mine.

I also have the same issue as you mentioned ealier and the same exact two monitors. I have an M4 Pro Macbook Pro - and got them to work for a whole week (both at 120hz 4K), but now suddenly they refuse to work again. They work just fine on my Macbook Pro M1 Max.

Did you ever start that other thread?

My new Macbook PRO M4 STOPPED recognizing my external Monitor. Worked for the past 2 months with no problems.

I used my computer with another HDMI cable connected to a projector and it worked great.

I came home, and now my External Monitor is no longer being recognized.

With or Without an external hub.

With the internal HDMI plug....I have tried everything....

Sometimes it works other times it does not.

More often does not work

I even got it to recognize the Same external Monitor Twice - once with the internal HDMI and with a HUB>

I have tried Resetting everything......NVIDIA, PR, sometimes it works for once -goes to sleep no recognition when it wakes.

help....is it related to the recent update last week????????

Howard

PLEASE HELP !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

My 2017 MacBook Pro worked great with the external monitor.