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

I have M1 Mac Mini 16GB, two screens

main Display

27 inch RAVEN MTi2 1920 x 1080 on HDMI

49 inch extra wide Samsung C49J89x 3840 x 1080 on USB-c->Displayport cable.

Big Sur 11.1 Issues

1) With both screens plugged in and the Mac rebooted both screens display black screens

2) With just the HDMI plugged in, a reboot goes all the way to Login, I plug in the second screen the USB-c -> displayport cable it wakes up as the second screen..

3) it does not matter if I use "Uses separate Display spaces" or not with two screens physically plugged in I fail to Boot.

pretty fundamental...

If I have the screens set to black solid colour, all well and good.

If I use the stock screen wallpaper and reboot to the login screen, I get a little dancing display of small pink rectangles, a bit like the old school video memory overlapping the system ram.

I will return as faulty if these issues are not fixed by an update.

Looks like 11.2 Big Sur RC has been released and wondering if anyone has tried it. I'm seeing this issue with my new M1 Mini too. Dual displays, one HDMI -> HDMI (HP 27"), one USB-C -> DP via OWC Thunderbay 3 DP port (Eizo 27"). Everything was the correct 2560x1440 60hz on initial setup. First time the mini went into sleep mode and I logged back in the Eizo switched to 1080p resolution. Restarting and disconnecting and reconnecting "fixes" it but as soon as it sleeps again it downscales again.

you can use Automator and create an app that force both monitors to startup and place it on the startup apps list. now every time you come back from sleep it execute the automator command and after a small flickering you have your monitors ready for work. try it out

I'm afraid I have to revise that. The flickering is back again. I have now tested on the DVI to HDMI. That works, but then only with 30 Hz. Apple needs to fix the firmware. Thanks Apple!

Acer CB281HK:

  Auflösung: 3840 x 2160 (2160p/4K UHD 1 - Ultra High Definition)

  UI sieht aus wie: 1920 x 1080 @ 30.00Hz

https://support.apple.com/en-ie/guide/mac-help/mchl7c7ebe08/mac

try this look for extend desktop,

Update again. I used a USB-C to VGA cable and the monitor now stops working when I put the Mac mini to sleep. A full restart will reset the monitor until it goes to sleep again. Hopefully they'll get this fixed. The direct HDMI monitor works no problem. It's only the second one that's the issue.

But why is the problem then only solved when pulling the HDMI cable from the HDMI port and not when pulling the USB-C cable from the USB-C port? I don't see why the problem would be the USB-C to HDMI adapter?

(I know, the other solution is also toggling the display resolution or also refresh rate)

That Display-Port Cable: https://www.amazon.de/dp/B07RY75V7Q/ref=cm_sw_r_cp_api_fabc_x8aYFb2PNFV28

and this HDMI Cable:

https://www.amazon.de/dp/B075V5JK36/ref=cm_sw_r_cp_api_fabc_h9aYFbKSJS1DA?_encoding=UTF8&psc=1

the other HDMI to HDMI-cable supports HDMI 2.1 🤔

I will order this cable from Amazon and try.

Anker USB C to HDMI Cable for Home Office, 6ft Type C to HDMI Adapter Supports 4K 60Hz, for MacBook Pro, MacBook Air, iPad Pro, Surface Book 2, Galaxy S20, and More https://www.amazon.com/dp/B07DBZYM8C/ref=cm_sw_r_cp_api_glc_fabc_fJsZFbJMGV94Q

Yes, I know. But USB C to HDMI also didn't work for some people (including me). It looks like it depends on the type of cable or adapter we are using. I think I'm gonna try this one first (USB C to DP) and then go back and try another USB C to HDMI if that one doesn't work.

I'm having the problem with the USB-C VGA adapter and also unplugging that adapter and reinserting it fixes it. Apple tech told me it's because when you do that it resets the SMC. I don't know what that means, but that's what they said.

Im happy that it worked for you, but I did the exact same thing. I erased the Mac completely, downloaded and reinstalled MacOS through the terminal with the help of the Apple Support (because a M1 specific personalization Error accrued, so the installation must be made through the Terminal). It took me two days of unsuccessful tries, until I wrote with an Apple Support Specialist, who knew this Problem and solved it with me) I wouldn’t recommend to do that because of this particular Display issue. (your problem seemed to be a bit different with that crashing)

So apple asked that I return the unit and upon receiving it, they would ship me another one Dec 30th! I opted to just purchase a second one then return my current one as close to the return deadline as possible so I can get a 100% refund. Truth is, even with this annoying display problem, the machine is so fast, almost shockingly so, that there's no way I can go back to my 2015MBP for the month.

So yeah... if you choose to return it, and it's a 16GB 512SSD version, you're looking at a couple weeks without your mini... unless you just buy another one and carefully pay attention to your return window.

luck!

Just tried out a DP 1.4 cable but nothing has changed. Fyi: I deleted my Mac before and installed Mac OS again with no success. I also delated these „plist“ files in applications (mentioned by kimac) together with the Apple support. It’s definitely a software problem and I wouldn’t recommend restoring your Mac because it doesn’t change anything.