Mac recognizing dual external displays as one monitor

With one minor exception, the same rules we learned for the M1 and M2 still apply to the M3 models. Display interfaces are generated deep inside the system on a chip. How many there are depends on the exact type of Processor:

M3 (plain) like the 13-in and 15-in supports up to ONE External fully hardware-accelerated external display. Except the M3 MacBook Air models with 13 or 15-in display, which can support a second external display instead of the built-in display when you close the cover on the built-in display. (...and power must be connected.)

M3 PRO processor supports up to Two fully hardware-accelerated external displays.

M3 MAX processor supports up to Four fully hardware-accelerated external displays.

Tech Specs now available here:

MacBook Pro - Tech Specs - Apple

MacBook Pro - Tech Specs - Apple

The M1 MacBook Pro only supports one external monitor.

If you are using DisplayLink technology, you can attach more. DisplayLink requires not only a third-party software driver on the computer – but a DisplayLink implementation (chips and software) in the hub/dock or monitor that's going to implement the second video port or display. The driver creates a virtual software display, and then sends updates to that display to the matching hub or monitor over a data connection. So it's not as "first class" as direct monitor support in the M1's GPU, but it might work out for many productivity applications.

Looking at Dell's site, I see no indication that the WD22TB4 supports DisplayLink technology. I think it is counting on the fact that a Thunderbolt connection can carry two DisplayPort sessions. (Aside: This is something that the LG 5K and Apple 5K/6K displays rely on. They use both sessions, each carrying the signal for half of the display.)

Unfortunately, while the M1 chip is sophisticated enough to support a single 5K or 6K monitor, it does not appear to be sophisticated enough to support two independent monitors using either DisplayPort chaining or the two Thunderbolt / DisplayPort sessions. That's reflected in Apple's specifications, which say that the 13" M1 MBP supports a single external monitor, and that it has Thunderbolt 3. (Thunderbolt 4 certification would have required the machine to be able to drive two external displays.)

https://www.dell.com/en-us/shop/dell-thunderbolt-dock-wd22tb4/apd/210-bdqh/pc-accessories#techspecs_section

There may be other hubs that you can attach to your Mac that would support DisplayLink technology and would allow you to have a second monitor (using compressed video sent over USB-C). The Synaptics site lists some of them.

https://www.synaptics.com/products/displaylink-graphics

Just be aware that DisplayLink is not the same thing as DisplayPort. DisplayPort is a standard for the direct connection of a display to a device (computer, tablet, etc.), whereas DIsplayLink is a clever workaround for when your hardware doesn't support as many direct connections as you'd like.

I really wanted to use dual 8k monitors. I asked my Apple salesman in Manhattan Beach, CA "Does this MacBook support dual external 8k monitors?" He had me wait while he went ask someone in the back. He came out and said "Yes, of course it supports dual 8k monitors." and I spent almost $5000 thinking that was what I was getting.

I feel so used and stupid!

Hello Shabiizz,

The reason you'd only be seeing one monitor in the display settings is because that computer model only supports one external monitor.

MacBook Pro (13-inch, M1, 2020) - Technical Specifications

Cheers!

The issue I was having with the two monitors is because I was using a Dell WD22TB4 Docking station which has two DisplayPorts an HDMI and some USBC thunderbolts. However I was using one DP and one USBC to hdmi converter cable in the USBC thunderbolt. In the Dell documentation it says the UCBC and HDMI port are multiplexed together so you cannot use both it’s one or the other. Then I bought a different adapter cable so one DP and one USBC to HDMI and it’s working great with two monitors now. I knew it should work cause I also use a 39” curve screen which is basically like the same data rates as two monitors. So check the user manual of the docking station it was kind of hard to find this information though.

Shabiizz Said:

"Mac recognizing dual external displays as one monitor: [...]he problem is both monitors are on. and showing the same display as each other..[...]"

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Try Un-Mirroring the Screens to your Mac:

Hold Down: [command + F1] or [command + dim screen button]

PROVIDED your Mac already supports multiple external displays... if you want to use a Dock:

TWO displays up to 4K each can only be supported on ONE cable out of the Mac when the PORT, the Cable, and the first device (Dock or Display) are ALL genuine ThunderBolt devices.

USB has only half the data pathways, and half the bandwidth of genuine ThunderBolt. The Mac does NOT support TWO displays over USB, and makes no apologies for its higher standards. Many Dell docks are NOT Thunderbolt, but USB-C Docks, and only support multiple displays when used with Windows.

I am using Macbook Pro M3 Max with Dell WD22TB4 docking station and facing the same issue with two Dell 4K monitors (U2720Q). I have tried to use many configurations e.g.two HDMI cables, one USB-C thunderbolt with one HDMI, both Display cables. Still facing the same issue.

Any “work arounds” you might find in the online space will likely be perceived as painfully deficient.

If your MacBook indeed lacks the fundamental ability to calculate the pixel positions for multiple external monitors … well … it’s a difficult shortfall to overcome.

MacBook Pro (14-inch, M3, Nov 2023) - Technical Specifications - Apple Support

More reading:

https://www.macrumors.com/2020/11/24/m1-macs-able-to-run-six-external-displays/

I’m having this same issue with MacBook Pro m3 pro the monitors only do the same thing tonighter not able to split into two in only reads one in the display settings did you ever get round it

So u need to extend the display into dual monitors right ! You are using the wrong dock then,only "dell universal d6000" docking station can do that or the updated model of d6000 that is "UD 22" i font know more abt it. But currently i sm using universal d6000.

I just had this issue with an older MacBook Pro and a WD22TB4 Dell. I was surprised it wouldn't do two 32" 1080 monitors because I run a 39" curve on it with cad and video editing same time no issues.

on the back of the dell it has two display ports, one HDMI and one display port labeled USB C port. first issue was that I couldn't run the USB C [dp] and the hdmi at the same time, turns out the Dell manual says it MUX's these two ports together so you only get one or the other. I just happened to not have an extra [dp] to cdmi connector so thats why I was doing a bunch of weird stuff to get this working, so I got that working for my windows computer but then plug in the MacBook and it only does mirror two external monitors (or extend but both are mirrored). turns out, there is another USB C port on the back of the dell with the lightning bolt symbol, this is actual thunderbolt that passthrough to the Mac. So I used that and it works. idk if my MacBook is an M1 this was a 2015, I dont think it is, but this post came up so I wanted to answer for that search results also. Also I tested my MacBook by running two monitors through just the USB C to HDMI adapters and it works that way so I knew it should work but was blaming the Dell Hub. Cheers.

Re: “… [To] Apple salesman in Manhattan Beach, CA ‘Does this MacBook support dual external 8k monitors?’ … ‘Yes’ … “

That’s a truly unfortunate in-store experience as the specs for multiple external monitor support is clearly published for each device.

If he/she had only looked …

the Mac does not support two hardware-accelerated displays on a USB port or cable.

Only on a genuine Thunderbolt Port, Cable, AND Thunderbolt Dock (or Thunderbolt Display with ports that can chain to a second display).