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I have an M1 Macbook Pro. I just found out it doesn't support HDMI 2.1. Because of this, it can not display 5120x1440 on my Samsung CRG9 (the CRG9 supports 5120x1440). My M1 Macbook Pro will only display 3840x1080: I've tried

  • Going direct with HDMI
  • And, with a Thunderbolt 4 dock that has an HDMI port and connecting the Thunderbolt 4 dock directly to the monitor.

My question is about other solutions. Is there anything that will support TRUE 5120x1440 via a dock?

Definitions,

  • By "support" I mean can be made to work with the hardware. I do not expect official support in any capacity from Apple on things they didn't extract a massive profit margin on.

  • By "true" I mean not downscaling. In OSX terms, "native" which is weird and I'll never say that. The CRG9 can be displayed with true 3840x1080 on the M1. BetterDisplay has the ability to

    • Create a 5120x1440 "Dummy Display", this gives you the right amount of real estate.
    • Mirror the Dummy Display onto real display. The signal going out to the monitor is still 3840x1080, but everything is "smaller" (and more blurry or as OSX likes to call it "scaled").

    That is to say BetterDisplay is not adding support for "True" 5120x1440.

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  • If you check Mactracker, your mac does not support that resolution, how will going indirect help?
    – Solar Mike
    Commented Mar 13, 2023 at 16:17
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    It's not really a '5k' display, it's 5k wide but only half deep. it's like 2 x 2k 27" side by side. It's not 'retina' either. It's a funny old animal, really.
    – Tetsujin
    Commented Mar 13, 2023 at 16:23
  • @Tetsujin I removed "5k" to eliminate confusion.
    – Evan Carroll
    Commented Mar 13, 2023 at 16:24
  • OK. We seem to get these questions a lot. Macs just don't seem to like these funny ultra-wide screens. Not sure there's a definitive answer.
    – Tetsujin
    Commented Mar 13, 2023 at 16:27
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    @DavidAnderson the right-most answer to that is because I'm using HDMI Matrix switch. The reason why is because EDID passthrough HDMI doesn't require remuxing since EDID is a separate channel from the video stream. This means that computers do not know when they're disconnected and reconnected from the Matrix switch. With DisplayPort, I don't think any does EDID emulation. It's far more complex.
    – Evan Carroll
    Commented Mar 13, 2023 at 17:18

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After working on this for a solid two weeks, and investing hundreds of dollars into it, I can say it's possible. And, even better -- I can confirm it will work through a Thunderbolt 4 Dock. I'm using the Lenovo Thunderbolt 4 Workstation Dock. I needed two things to make this work,

Here is the bottom line: the HDMI on the M1 is simply crippled. Not sure if the crippling is in hardware or software. You can read this from author of BetterDisplay,

Yes, M1 macs have severe limitations when it comes to HDMI connections and non-16:9 displays Even on 16:9 4K displays they seem to arbitrarily limit resolutions to a certain degree. Apple seemingly tested/optimized HDMI support to suit some 4K TVs only, but not for computer monitors, that's why it is best to use DisplayPort (or USB-C which internally uses DisplayPort). An other route (if you insist on using HDMI) might be to use EDID (this is the data the display reports about itself to the computer) override to convince macOS that the display is DP instead of HDMI, that might enable 5120x1440 via the Thunderbolt dock (not the built-in HDMI though) - this is possible, because a thunderbolt dock actually uses DisplayPort (data) to communicate with the Mac and Apple Silicon Macs take what the display reports about itself (is it HDMI or DP?) in its EDID for granted whether it's a HDMI or DP (if no data is given, then it probably checks the DPCD data to figure out if behind a DP dongle or dock there is HDMI or not).

You basically have to

  1. Extract the EDID of the desired monitor,
  2. Modify the EDID (you can use the free AW EDID Editor), instructions taken from here
    1. Ensure that DisplayPort 1.4 is enabled in EDID, if not set it
    2. Ensure that that EDID Revision 1.4 is enabled.
  3. Overwrite the EDID for the monitor when plugged into the USB-C to HDMI 2.1 Adapter. For this, I used BetterDisplay.

This should enable the desired Low-PPI resolution of 5120x1440.

Proof with OSD of 5120x1440 on OSX

A huge thanks goes out to the author of BetterDisplay, waydabber, for supporting me through this process BEFORE I purchased BetterDisplay. Huge thanks. Inspired by his response here.

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