How do I get my MacBook Pro to recognise two external monitors connected through a docking station?

AndrewL_01 wrote:

I have a variation of this problem I think. I have two HDMI monitors connected to an Anker USB-C dock and a MacBook Pro. This all worked perfectly until I allowed the MacBook to upgrade to Tahoe. Now it treats both of the external monitors as one. I used to be able to extend my desktop across three screens, internal and two external. Now I just get a duplication of one external monitor's view on both.

So to recap: the hardware hasn't changed, the cables haven't changed. The OS has. And now it doesn't work as it should/did.

What specific "Anker USB-C dock" is this?

Macs do not support connecting two monitors to a plain USB-C dock. They only support connecting two monitors to a Thunderbolt one.

Any non-Thunderbolt dock that allows plugging in two or more monitors at the same time would be using

• DisplayPort MST – which the Mac does not support. (Typical symptom: the Mac only sees one display, and all displays seem to mirror each other), and/or
• Some second-class "workaround" like DisplayLink that requires the installation of a special driver and that can break if the operating system changes

Looking on the Anker site, while I see one or two Thunderbolt hubs, most of the hubs appear to be of one of the other types. The description of one of those had a "Note: This product is not recommended for MacBook users who wish to connect dual monitors with different displays. For macOS, the external monitors will display identical content." – confirming that that particular USB-C hub relied on DisplayPort MST.

https://www.anker.com/collections/hubs-and-docks

Grant Bennet-Alder wrote:

if THIS is your $400 docking station:

ALOGIC PRIME DX2 Universal Dock - Connects monitors, networks and accessories - Space gray

https://alogic.se/en/products/alogic-prime-dx2-universal-dock-w-dual-4k-and-with-100w-pd

... it has only a USB-C input, and can not provide Full Motion Video to two displays when connected to a Mac.

Did you see this footnote:

This product requires DisplayLink Drivers, which you can download here:

 https://www.displaylink.com/downloads

If that is the product, 399.99 EUR is a lot to charge for a plain "USB-A/USB-C" dock that appears to rely solely on the second-class DisplayLink workaround. A currency converter site says that is roughly equivalent to $470 USD, which is a lot more than many genuine Thunderbolt docks go for, with sales tax and shipping!

I couldn't find any hint that the dock even takes advantage of DisplayPort Alt Mode (which the Mac does support) for one output, when available; or that it takes advantage of DisplayPort MST (which the Mac doesn't support over a plain USB-C connection). Some "universal" docks will take advantage of DisplayPort Alt Mode when available – but, of course, since USB-A was never designed to carry video, they all rely on second-class workarounds at least some of the time.

https://alogic.co/pages/knowledge-base does not have a lot of detail, but says that "The DX2 uses the DisplayLink chipset and requires the DisplayLink software to be installed on the connected laptops." It also says that while the DX2 is "compatible with devices that have Thunderbolt 3 or 4 ports", "it won't be able to achieve Thunderbolt data rates" – confirming that the DX2 is not a Thunderbolt dock.

skippybaxter wrote:

So I have a MacBook Pro 2024 model on Tahoe 26.2. I have recently purchased to external monitors hooked up to a alogic docking station. It is only recognising 1 display monitor not 2. How do I fix this? I've spent nearly $700 on these displays and recently spend $400 on a docking station.

[Re-Titled by Moderator]

Original Title: external monitor issues

What happens if you plug direct into the Mac...?

the game keeps changing yes.

The newest macOS are increasingly fussy over sub-par cables for connecting external displays.

Recommended high quality cables: certified Ultra HDMI or Premium ≤ 1.0 m length

or USB-C Thunderbolt5 cables ≤ 0.5 m length cables rated for high speed data.

certified (Thunderbolt logo on each end)

The current stable release of Tahoe including bug fixes, security updates is macOS 26.3

Keep your Mac up to date - Apple Support

https://support.apple.com/guide/mac-help/get-macos-updates-mchlpx1065/mac

A 16” MBP with a hardware model year would have either a M4 Pro chip

or a M4 Max chip.

In the former case, the MBP could support up to two external displays. In the latter, it could support up to four.

In either case, it could drive at most one display over a plain USB-C dock; two over a Thunderbolt one.

if THIS is your $400 docking station:

ALOGIC PRIME DX2 Universal Dock - Connects monitors, networks and accessories - Space gray

https://alogic.se/en/products/alogic-prime-dx2-universal-dock-w-dual-4k-and-with-100w-pd

... it has only a USB-C input, and can not provide Full Motion Video to two displays when connected to a Mac.

Did you see this footnote:

This product requires DisplayLink Drivers, which you can download here:

 https://www.displaylink.com/downloads

DisplayLink technology creates a "fake" display buffer in RAM, sends the data out over a slower interface to a stunt box with DisplayLink custom chips that put that data back onto a "legacy" interface. It is not a true "accelerated" display, and it can suffer from lagging. Using a Mouse on a DisplayLink display can produce nausea.

Just adding the DisplayLink Driver is not adequate to get a picture -- you need a DisplayLink "stunt-box" or a Dock that includes DisplayLink chips. NB>> j5create has produced their own versions.

————

It may be acceptable for a second display showing slow-to-change data such as computer program listings, stock quotes, or spreadsheets, but NOT for full motion Video, not for Video editing, and absolutely not for gaming. Mouse-tracking on that display can lag, and can make you feel queasy.

In a pinch, it may even play Internet videos (as one user put it) “without too many dropped frames".

If you are only doing program listings spreadsheets, stock quotes, and other slow to change data, DisplayLink can work for you, but requires you to make some strong compromises.

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It is really nice to know that you can use a DisplayLink display if you MUST have an additional display for some of the types of data I mentioned. But that is NOT the same as the computer supporting a second, built-in, Hardware-accelerated display.

These displays depend on DisplayLink software, and are at the whim of Apple when they make MacOS changes. There have been cases where MacOS changes completely disabled DisplayLink software, and it took some time for them to recover.

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I think the Big Surprise for a lot of Hub/Dock buyers is that they thought they were getting a "real" display, but actually got a DisplayLink "fake" Display. If you got what you expected in every case, I would not use such pejorative terms to describe DisplayLink.

Which “alogic docking station’?

That can depend on the kind of docking station and the capacity of the device to support dual monitors. If you're able to connect one to the device directly instead of through dock station that may help.

<< not sure about Macintosh compatibility. >>

most PC-centric Docks from Microsoft, Dell, HP and others have support for Windows on PC systems, ONLY. If you get stuck for any reason, and need support, their spec sheets claim support for Windows versions ONLY. They often support only specific models of same-Brand computers. If a firmware upgrade is ever needed, a recent Windows system is required to install that upgrade some require additional software running on your windows system to operate correctly.

[in my opinion] very few of these will ever work properly on a Mac, unless the specs Explicitly say they support Macs.

I have a variation of this problem I think. I have two HDMI monitors connected to an Anker USB-C dock and a MacBook Pro. This all worked perfectly until I allowed the MacBook to upgrade to Tahoe. Now it treats both of the external monitors as one. I used to be able to extend my desktop across three screens, internal and two external. Now I just get a duplication of one external monitor's view on both.

So to recap: the hardware hasn't changed, the cables haven't changed. The OS has. And now it doesn't work as it should/did.

Ok, thanks for the input. Very helpful. Maybe I was mistaken about the extended desktop working properly under the previous OS. TBH I’ve only had one external monitor connected to the dock most of the time in recent months. Just plugged the 2nd one back in this morning expecting it to work the way I thought I was used to and it didn’t.

I guess I could try and revert the OS to double check. But from what you’re saying it sounds like that might be a waste of time and effort.

I had a similar challenge with old Elgato Thunderbolt #2 dock, this has two thunderbolt 2 ports (same connector profile as mini display port) and one hdmi port. Don't have a mac that works with that anymore had to recycle old macbook pro because battery went bad. I can't remember if I ever got this to support two displays at the same time through the dock, I don't think that ever really worked too well for that if it did.

New dock I got for windows surface pro is a USB4 Dock for business, this might be compatible with Macs that have usb-c not sure. This does claim to support dual 4k monitors and usually retails for about $200 u.s.d. Microsoft has a more expensive "Thunderbolt 4" option which costs $300 and has more features, not sure about Macintosh compatibility.