Mac recognizing dual external displays as one monitor

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Mac recognizing dual external displays as one monitor

Hi all,

I am using a 2019 15-inch MacBook Pro and running version 11.1 of Big Sur. At work, I have been able to connect my computer to a dock that is connected to two displays and use those two displays as one extended display. I am trying to replicate that setup at home and am having some issues. My Mac is recognizing both of the external displays, but it is acting as if the external displays are one display, so the two external displays are mirroring each other and my mac is the extended screen. I want to have the two external displays have an extended display, and not just mirror each other. When I go to arrangement under system displays, it is only showing two screens, while I would like to see three.

Following are the products I am using:

2 BenQ monitors and the HDMI cords they came with: https://www.amazon.com/gp/product/B072XCZSSW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Elecife USB-C hub: https://www.amazon.com/gp/product/B08CGYXSBK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Thanks in advance!

Posted on Dec 27, 2020 8:30 AM

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Answer 1

Top-ranking reply

genno01 Author

Level 1

21 points

Dec 30, 2020 2:23 AM in response to Grant Bennet-Alder

Hello, the two monitors are showing up on the arrangement screen as one, there is no overlap and I can’t separate them. After reading through the comments, I believe that the issue is my dock, but thank you for your help!

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Answer 2

Dec 29, 2020 2:05 PM in response to genno01

The ‘problem’ is your hub. The $30-100 ones that you find on Amazon don’t really support >1 external desktop. This is from the Amazon link you provided:

As you see, only one extended desktop.

Docks that properly support dual displays on a Mac are those from OWC, Brydge (Stone Pro), Elgato, Belkin and Kensington. The least expensive one I’m aware of is the OWC thunderbolt 3 mini dock, was $120 last time I checked.

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Answer 3

genno01 Author

Level 1

21 points

Dec 29, 2020 1:08 PM in response to Matthew.S81

Hi Matthew,

Thanks for your response! So when I am looking at the arrangements tab, it is considering both of my monitors as one for some reason (when I click on the display it even highlights a red ring around both monitors). I actually just ordered an HDMI to USB C converter, though, and I am planning on seeing if that works! I will keep this thread updated when I receive the converter!

Thank you!

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Answer 4

Dec 29, 2020 11:29 AM in response to genno01

Hello, genno01.

Thank you for using Apple Support Communities.

From your post, we understand you're trying to get your external monitors to be in extended mode. We'd be glad to help out. Check and make sure that Mirror displays isn't checked: Use external monitors with your Mac

"Use extended desktop mode

Choose Apple menu  > System Preferences, then click Displays.
Click the Arrangement tab.
Make sure that the Mirror Displays checkbox isn’t selected.
Arrange your displays to match the setup on your desk. To change the position of a display, drag it to the desired position. A red border appears around the display as it's moved.
To set a different display as the primary display, drag the menu bar to the other display. The primary display is where your desktop icons and app windows first appear.

If that's not the issue, are you able to connect one monitor directly to the MacBook Pro? If so, does extended display work as expected?

See if the same thing occurs in safe mode: How to use safe mode on your Mac

Keep us updated.

Cheers!

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Answer 5

genno01 Author

Level 1

21 points

Dec 30, 2020 2:22 AM in response to neuroanatomist

Ahh, I see! I didn’t even look at that graphic before and had instead read the section where it said “triple display with OS”. I think you are completely correct and I will look into getting a better quality dock, such as one of the ones you suggested. Thank you!

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Answer 6

Dec 29, 2020 3:09 PM in response to genno01

When you have more than two displays that are actually completely independent (not hampered by a Dock that cannot support both as independent displays) you can mirror any combination of them.

If your Arrangement tab shows two displays that are nearly, but not quite, coincident, that is a hint that those two displays are mirrored. Select one or the other and drag them apart from each other.

Remember that they need to end up sharing an edge with another display. If you drag one too far away, they may just snap back the way they were.

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Mac recognizing dual external displays as one monitor

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