Mac Mini (M1) dual display doesn't work.

I have an update to my situation. Now the problem is solved with my new (temporary) settings.

Original settings:

• 2 external monitors (LG: 24MK430H-B & 22MK430H-B) (Same model, 24in & 22in)
  • https://www.lg.com/ca_en/desktop-monitors/lg-24MK430H-B-led-monitor
• Mac Mini>USBC-to-HDMI adapter(Belkin)>HDMI cable>LG:24in & Mac Mini>HDMI cable>LG:22in

///// Change: I replaced my LG:24in monitor with a new monitor (LG: 27UD68-W) and replaced USBC-to-HDMI adapter & HDMI cable I was using for this monitor with a new USBC-to-HDMI cable.

Current settings:

• 2 external monitors (LG: 27UD68-W & 22MK430H-B)
  • new monitor: https://www.lg.com/us/monitors/lg-27UD68-W-4k-uhd-led-monitor
• Mac Mini>USBC-to-HDMI cable(j5create)>LG:27in & Mac Mini>HDMI cable>LG:22in
  • new cable: https://en.j5create.com/products/jcc153g

Since I changed my settings I've restarted my computer more than several times but I'm not experiencing the issues even once. I am now ordering another cable (QGeeM: USBC-to-Displayport cable)(https://www.amazon.ca/gp/product/B074V5MMCH/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1) to replace my USBC-to-HDMI cable(j5create) due to an unrelated laggy mouse issue, so once I receive and replace it I will post another update explaining whether it's working or not.

Are u sure your j5create cable is capable of 4k60fps? If it’s not, it passes 4K with 30fps through, that would explain your laggy mouse and maybe that’s also the reason why you couldn’t reproduce that issue with that cable. I also don’t think your new cable will fix this, because I use the same one 😕

I also heard from my friend, who uses same Mac mini with multiple display, could use this cable.

https://www.amazon.co.jp/gp/product/B01LXPOIRM/ref=ppx_yo_dt_b_asin_title_o00?ie=UTF8&psc=1

Only the common spec I can think of in between the adapter I posted earlier and this cable is both DP1.4 compatible. I think many people here posted DP adapter or cable link, but I think most of them were not DP1.4 compatible. Again cannot guarantee but this is my guess.

I've just received this exact cable and it does not work!

I am using 2 x Apple DisplayPort 27 inch Cinema Displays. One is plugged in with a DP to USB C adapter and working fine. Just tired adding another display using that connector and it does not work. Here is the output of the system profiler.

I wish you could use multiple DP adapter via USB c like in the Intel Mac Mini.

I will probably try the DisplayLink adapters next

Long time apple user, first time forum commenter.

I wanted to provide my experience of my M1 Mac Mini. Short version is that Apple support told me that a USB-C to HDMI or DP adaptor is not going to work (which includes the A2119 adapter that they sell - For reference if you only are using one screen it's fine, but it will NOT play nice with multiple displays) and that you MUST use something that's thunderbolt supported.

I ended up buying the Belkin Thunderbolt 3 Dock (F4U095AU) your milage may vary in different parts of the world given I think this was sold in AU. Using a Display port to Display Port cable that I got off Amazon I now have 2 screens at the same resolution and refresh rate. For anyone interested, this is my setup:

There is one catch, where no matter which screen i have setup for "primary" the displays always seem to reset to my "secondary" display always being on the wrong side (it thinks I have to mouse right instead of left) but aside from that small inconvenience, I have no flickering, and no other issues. But the engineering guys were very specific in saying that running 2 monitors using a USB-C adaptor and HDMI won't work at all.

Hopefully this information helps someone out so that they aren't tearing their hair out like I was!

Totally agree with you kibble4. I'm just telling you what works for me as I know how much time and effort (and money) I've sunk into getting things to work. This is just one solution of many that I'm sure that will work so don't shoot the messenger. I just hope it stops people from tearing their hair out cause I wished that I knew what adapters worked out of the box instead of having to guess! And i really thought that the "Apple sanctioned" A2119 adapter would help me function with a second screen (that was a waste of AU$80). I've seen a post about some displaylink adapter working that gives you 6 displays (https://www.macrumors.com/2020/11/24/m1-macs-able-to-run-six-external-displays/ ) not condoning the solution because I haven't personally tested it, but it was an interesting read.

My anker usb c to hdmi cord didn’t help. I have one advertised as 1.4 in the mail. My latest effort is to create an Automator action that runs at startup and changes the refresh rate. Which is the only fix I can find to fix the problem.

Just adding my 2 cents and experiences here (have the EXACT same problem as everyone)...

1. Have M1 Mac Mini (16GB/512GB FWIW, but don't think it matters). Mac OS 11.0.1.
2. Have two Lenovo Q27 QHD screens, identical - they have HDMI + DP inputs.
3. Used high-quality HDMI 1.4 and HDMI 2.0 cables, HDMI to HDMI.
4. Used TB3 to HDMI (ver unknown, assuming <= 1.4), TB3 to DP, single cables, adapters, dongles, etc.
5. Not listing out all the various adapters but they are reasonably high-quality; none are Apple-branded.
6. All of these cables, dongles, adapters, etc. work perfectly in a Windows 10 multi-monitor environment.

Problem = upon screen wake (and I even have the "don't sleep when screens are off" checked in the Energy panel), one and/or both screen(s) will flicker, be unresponsive, stay black with no background, etc. This happens when Big Sur sets the monitors to different refresh rates. Sometimes the BT mouse will work well so I can just launch Displays, change the offending monitor's refresh back to 60Hz, and re-arrange, but sometimes not. The other solution is to manually turn off the "black" screen, turn it back on, which triggers something that fixes the issue (still need to re-arrange, but at least Big Sur recognizes the screen).

My conclusion = definitely a software bug/issue. Apple needs to fix this and I presume they will given all the noise/experiences/feedback from the user community.

My work-around solutions = launch Display panel if you can, gather windows, set refreshes back to same Hz, re-arrange. If that doesn't work, turning off the offending monitor and turning it back on has the same effect as plugging/unplugging the monitor's cable and forces Big Sur to re-recognize the screen. Then open Display panel and re-arrange.

This is annoying but at least I can work on 2x screens for now. I turn off sleep which consumes more power of course, but that's a relatively small price to pay vs. just using one screen, and I hope Apple fixes this soon.

I do the same now every time I reboot. After a reboot both monitors flicker. I change their default resolution from 1920x1200 to 1920x1080. They stop flickering then. I can then change them back to 1920x1200 and it operates without a flicker. BUT, when it restarts next time, I'll have to do the same all over again. I'm also experiencing the dreaded bluetooth problem where it doesn't recognise my wireless keyboard, so I'm now back to using a 10-year old wired unit!

Mac Mini M1 - Dual Displays (problem fixed?)

Try unplugging all display connections. Plug in the USB-C to HDMI first. Once that screen is up then plug in the HDMI to HDMI.

Seems to be sustainable but will continue testing.

Yes... thanks, but there was another issue I encountered with browser memory causing a restart of the browser - when using Safari only one window on a Google video call. I am a little concerned about a few things. I doubt there are hardware issues, but there could be with a new architecture - who knows? The machine is useless to me if this happens. I just came here to see if I was not alone. I need to teach a class with it, and can't have it go down again. I'll wait 2 months... and re-order. Thanks...

Exact same issue here with two 4K monitors. Interestingly system information identifies monitors correctly as 3840 x 2160 but when setting up each monitor and choosing monitor’s native resolution, it is definitely something waaay less than 4K (more like 1080). I have several different brand ultra high speed HDMI cables that I swapped in and out thinking it was that but no joy.

Besides that historic aspect, digibudII, the M1 based Macs use a completely different processor (the M1), that cannot run the native Intel code of Catalina, and previous macOSs built for Intel based Macs.

So I thought the problem was the HDMI cables. I was wrong. I took a VGA-to-USB-C adapter and connect the USB-C end to the back of the Mini M1 and the VGA end to the 2nd monitor. No more flickering.