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

On an M1 Mini, if you attach one display using the built-in HDMI connector, and then a DisplayPort or Thunderbolt capable display using the USB-C connector, it will work, yes

No. I ended up a 3 days of Apple customer support thru phone and they are aware of this issue. They told me and I quote: "wait for Big Sur 11.2 upgrade that's the only solution right now" The problem is specifically with the DVI connection to HDMI (cable or adapter) the only way that works right now is a monitor WITH a HDMI port on the back or a Thunderbolt port on the back, It only works with one monitor using HDMI and other using USB-C (from and to) so old monitors using adapters will never work until Big Sur 11.2

I WAS the one wrote:

On an M1 Mini, if you attach one display using the built-in

HDMI connector, and then a DisplayPort or Thunderbolt capable display using the USB-C connector, it will work, yes

No. I ended up a 3 days of Apple customer support thru phone and they are aware of this issue. They told me and I quote: "wait for Big Sur 11.2 upgrade that's the only solution right now" The problem is specifically with the DVI connection to HDMI (cable or adapter) the only way that works right now is a monitor WITH a HDMI port on the back or a Thunderbolt port on the back, It only works with one monitor using HDMI and other using USB-C (from and to) so old monitors using adapters will never work until Big Sur 11.2

Where did I say anything about attaching displays via adapters? Again, if you attach one display using the built-in HDMI connector, and then a second DisplayPort or Thunderbolt capable display using the USB-C connector, it works (modulo the wake from sleep problem).

I think the problem with the USB-C adapters is that the M1 Mini doesn't support HDMI over USB-C, which is what many of those adapters are doing. As for HDMI to DVI adapters, if you're having trouble with one of those, I'm not sure — HDMI is backwards compatible with DVI, though I don't think you can do dual link DVI from an HDMI port without active electronics (dual link DVI uses extra conductors, as I understand it, whereas HDMI increased the signalling rate instead), so that could be your problem there.

So far, the 11.2 update has fixed things for me. I'm not using adapters — I just have two LG 32UL750s, one attached via HDMI and the other via USB-C. I installed the update this morning (UK time, so it's been several hours already), and thus far it's managed to wake from sleep successfully a few times without forgetting one of the displays, whereas on 11.1 it would usually wake up with only a single display and refuse to detect the other one.

The only thing I did find is that while installing 11.2, my HDMI attached display spent a good few minutes flashing blue and black stripes at me; I was briefly worried that it was more broken than it had been before. So if you see that, don't panic!

It's a perfect storm of several things that nobody really appreciates, plus a couple of things that are obvious when you think about them. The obvious things are that previous Apple chips have been used in devices that have a single display, and that, as a result the ability to drive two displays is less well tested at this point (versus the Mac Mini, which had either a standard discrete GPU or for the Intel models an integrated GPU that was already in use in the PC market, where multiple displays are quite common).

The things nobody appreciates have to do with HDMI, DisplayPort and Thunderbolt, namely:

• HDMI, DisplayPort, USB (even over USB-C) and Thunderbolt are all different protocols; they are not natively compatible as is sometimes supposed.
• While you can get passive adapters that let you connect HDMI to DVI, DisplayPort to HDMI, USB-C to HDMI and so on, this works because of special compatibility modes built into the various standards.
• Compatibility modes generally can't be chained. For instance, a passive DisplayPort to HDMI adapter plus a passive HDMI to DVI adapter won't necessarily work. Active adapters may make that work in some cases — or they may not — depending on whether they implement the required compatibility mode support.

For instance, USB supports DisplayPort Alternate Mode, Thunderbolt Alternate Mode and HDMI Alternate Mode. Thunderbolt can carry DisplayPort (as well as having a compatibility mode for DisplayPort-only devices), so it's possible to have DisplayPort over Thunderbolt over USB. Physical DisplayPort implementations are likewise often "dual mode", and can switch to using an HDMI or single-link DVI signal when they detect that that's what they're connected to. But Thunderbolt and the USB alternate modes don't support that. To add further confusion, some devices with DVI connectors can output HDMI signals but out of a DVI socket (yes, they really are different; HDMI is compatible with single-link DVI, but not other variants). And for extra fun, higher resolutions and refresh rates might require either dual-link DVI or HDMI, and obviously some devices may support both kinds of input.

So, why does this all seem to work for PC owners? Honestly, it doesn't always. Many PC owners have been saved largely by the fact that their graphics cards still sport DisplayPort or HDMI rather than Thunderbolt or USB-C connectors.

An additional complication with the M1 Mini is that it doesn't support HDMI Alternate Mode on its USB-C ports. That means that passive USB to HDMI adapters won't work.

Finally, the data rates required by modern displays mean that there are plenty of old cables out there that won't work or won't work reliably. Usually the cables that come with your display should be OK. Cable vendors are supposed to indicate compatibility with the various standards (and the various data rates) using a set of fairly confusing symbols, which don't necessarily make matters much easier either.

Anyway, hopefully that's all helpful to someone :-)

But they do work (modulo the remaining wake from sleep issue) if they’re attached the way Apple specifies. That is, one HDMI display and one display over Thunderbolt.

The thing causing the most trouble for people in this thread is trying to use adapters of various sorts, and it’s confusing because naïvely it appears to make sense that they should. Unfortunately, the best intentions of the engineers who designed many of these standards (in terms of the various compatibility modes, some of which are optional) have in this instance backfired somewhat and created expectations of compatibility that don’t match reality. I wanted to explain some of that in the hope that it will help people understanding what will and will not work.

I agree that some of the bugs need to be fixed. But that still won’t help if you’re expecting to use adapters hanging off the USB-C port.

Just want to reiterate, I'm running at 100%, issue free now using the USB-C Multiport adapter from apple and an HDMI cable for dual monitor support. I was using a VGA multipart adapter before and having many issues. Just switching to the HDMI multipart adapter and updating to 11.1 Big Sur seems to have fixed it for me.. FWIW.

On an M1 Mini, if you attach one display using the built-in HDMI connector, and then a DisplayPort or Thunderbolt capable display using the USB-C connector, it will work, yes. If you have problems with display glitches, it's worth checking the cables as a lot of older or lower quality cables can't actually cope with the data rates required for high DPI displays.

Even then, though, there are some bugs, it seems, particularly when waking from sleep; I've been working around these by switching both displays off when I leave the machine, then when I return turning them both on and hitting the Shift key to wake it up. Without doing that, I routinely find that my Mini forgets about the HDMI display, and once that's happened, it takes a reboot to fix it (the Detect Displays button in the Displays panel in System Preferences doesn't fix it for me).

Confirmed!!! The beta of Big Sur 11.2 beta 2 fixed all my issues. Now running dual 4K monitors without issue. The flickering has stopped and It’s keeping the arrangement on restart now as well. Woot woot!

So knock on wood but it looks like 11.2 might fix this issue I was seeing. Installed it and did a couple of tests putting the Mac Mini to sleep and waking it up. Both times I tried everything was the correct 2560x1440 60hz waking from sleep with the same dual displays, one HDMI -> HDMI (HP 27"), one USB-C -> DP via OWC Thunderbay 3 DP port (Eizo 27"). Fingers crossed it stays this way!

I don't know if this may be helpful to anyone, but I just bought and setup my mac mini m1 and I had the same issues with my j5 create Dual HDMI Mini Dock for some reason the displays were mirroring and I could not get it to detect it as separate displays. So I tried my old iHome adapter display and that worked for me. So my setup is the HDMI cord in the back of the mini and I have my iHome USB-C adapter plugged in the back as well with my HDMI plugged in the adapter.

Hope this helps!

Plug in the hdmi screen only and reboot then use the usb-c to usbc(display port n monitor) and plug it in…. If it does not spark into life then shutdown Mini… press and hold in power button until the maintenance boot starts , shutdown then restart , that fixed it for me, I have a 27 touch screen as hdmi to hdmi and a Samsung 49 extra wide screen for the usb-c to usb-c (display port set as connection on monitor)

Mac Mini hdmi port ->hdmi in on monitor 1

Mac Mini usb-c -> usb-c in on Monitor (display port in)

no adaptors , just native cables

using 11.2 update

problem has been solved with Big Sur update, it wasn't the cables at all.

I had the same problem and on this site, I read that someone had no problem with a VGA to USB C adapter , so I bought one from Amazon : Belkin USB C to VGA adapter. I received today the problem is fixed works perfect with my LG low cost monitor

Good luck

A reasonably good analysis, Alastair Houghton. Thank you.

Another issue, in the mix, is that the “USB-C” connectors, on the M1 Macs—the ones with the Thunderbolt symbol—are actually USB4—the newest USB standard.

This new standard has its own “wrinkles”, with regard to various modes.

They are not to be confused with the old USB-C/Thunderbolt-3 ports on the Intel based Macs.

The main thing that will take time to catch-up to this change are the adapters and cables: there are, at least, three levels of cable compatibility, all with their own logos, which are supposed to help consumers know they have the correct products.

However, I have yet to see these logos displayed where they should be, let alone on sites where one may order such—even from Apple.

This is not, truly, the fault of Apple’s M1 based Macs—Apple is simply making this change contemporaneously with the M1 change, in order to be prepared for the future.

Unfortunately, however, the rest of Apple—let alone the rest of the computer industry—has yet to catch-up to this (coming) future.