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Adding a second external display to my M1 iMac

Apple tells me that my M1 iMac won't display to two HDMI external monitor/TVs. But it did so just fine from when I bought it last Spring until MacOS 12.3 came out. I have an unpowered USB bus with two HDMI ports. I want my two external displays to show the exact same screen.


The Genius Bar reinstalled MacOS (and then I had to restore from backup). They sold me two $70 HDMI adaptors, but only one worked at a time (so I returned one). I tried buying an unpowered USB-C to HDMI adaptor from Best Buy that my iMac did not recognize. I bought an unpowered HDMI splitter. MacOS just doesn't see the HDMI monitors anymore.


Is there any other way to mirror my two TVs (I use them for Karaoke)?


(I still can't tell this forum that my old computer was replaced last Spring).

iMac Line (2012 and Later)

Posted on Apr 8, 2022 8:00 AM

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Question marked as Top-ranking reply

Posted on Apr 8, 2022 8:10 AM

24" iMacs ONLY support 1 external display. Please refer to the Technical Specifications which are pretty clear iMac (24-inch, M1, 2021) - Technical Specifications

Please look in the section called Video Support. If you need a Mac that supports more than one external display then you own the wrong Mac.



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11 replies

Apr 8, 2022 9:20 AM in response to Howard Brazee

They have this product: https://eshop.macsales.com/item/OWC/CADPDL2HDMI/, that looks good for my needs. At $119, I expect to wait until the end of the month (and will return it if it doesn't work).


I noticed one of the features is on my $70 Apple HDMI card, the ability to recharge a Mac while using it. Not useful for iMacs like mine, I was hoping that that USB port worked the other way (to plug in a device).

Apr 12, 2022 5:16 PM in response to rkaufmann87

I needed to install https://www.synaptics.com/products/displaylink-graphics/downloads/macos, and allow it in System Preferences > Security and Privacy > General. I couldn't figure out how to get it visible there, but after I rebooted, when I tried to run it, it automatically showed up. Now, when I run it with other monitors attached, they show up and I can configure it. I tested it out successfully. Since I run karaoke night twice a month, I won't set DisplayLink to run automatically.
I then booted to my clone external drive, and installed DisplayLink there. But I even with multiple boots, I couldn't figure out how to get it in System Preferences > Security and Privacy > General.

Adding a second external display to my M1 iMac

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