The Mac mini 2018 (specs) has one HDMI port and four Thunderbolt 3 (USB-C) ports. It does not have any Mini DisplayPort (mDP) / Thunderbolt 2 ports.
Information below is for mini 2018 running Mojave, specifically 10.14.1
Thunderbolt 3 to Thunderbolt 2 Adapter Does Not Support Mini DisplayPort
Although on previous Mac models you could plug a mDP cable into a Thunderbolt 2 port and get a display signal no problem, the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter (MMEL2AM/A) does not support Mini DisplayPort output. It just doesn't work.
While this is indicated on the box as shown above, it is a substantial change from how users expect Thunderbolt 2 ports to work.
Two Thunderbolt 3 Buses
The mini 2018 has two Thunderbolt 3 buses, you can see them in System Information - Thunderbolt as Bus 0 and Bus 1.
I have not found any documentation of which port is on which bus, so I am assuming it is the same as on the iMac Pro. Note that this is only an assumption.
I have adapted a Thunderbolt 3 bus diagram from Connect multiple displays to your iMac Pro, section Connect to Thunderbolt ports on different buses. For the iMac Pro, Apple recommends "Use different Thunderbolt buses when possible".
Above diagram is speculative only, NOT OFFICIAL.
There is no similar guidance about displays and Thunderbolt 3 buses in the Apple Support article Connect multiple displays to your Mac mini (2018), so using different buses may not apply to the Mac mini 2018, but there is no harm in following this approach.
DisplayPort does not use Thunderbolt 3, so System Information will still show "No device connected" for all four Thunderbolt ports even when you have DisplayPort displays connected.
DisplayPort is a USB service; you will only see those connections in System Information - USB. Adapters will show up under USB 3.1 Bus as e.g. "USB-C Video Cable" or "USB-C to DP".
Working DisplayPort Configuration for Dual Monitors
The following configuration works:
- A Moshi USB-C to DisplayPort cable on Port 1 (Bus 0) to a Dell P2415Q primary monitor in horizontal (landscape) mode, at 3840x2160 60Hz actual, and 1920x1080 60Hz synthetic HiDPI resolution
- A CableMatters USB-C to DisplayPort cable on Port 4 (Bus 1) to a Dell P2415Q secondary monitor in vertical (portrait) mode, at 2160x3840 60Hz actual, and 1080x1920 60Hz synthetic HiDPI resolution
System Preferences - Displays - Arrangement gives an idea of the setup
The System Preferences - Displays panels are a bit confusing as they make it look like the monitors are using different resolutions (and also the vertical display doesn't show as rotated).
Note that you do not have to create a display override file for the Dell P2415Q to support HiDPI when rotated, it should just work.
If you want to see what resolutions the system is using, check System Information - Hardware - Graphics/Displays. It shows both the actual resolution ("Resolution:") and the synthetic HiDPI Retina resolution ("UI Looks like:") e.g. for the Dell P2415Q in horizontal mode it says Resolution: 3840x2160 and UI Looks like: 1920x1080 @ 60 Hz.
Mini DisplayPort Issues
As mentioned above the Thunderbolt 3 to Thunderbolt 2 adapter won't drive a mini DisplayPort connection.
I also could not get the mini 2018 to work correctly with two USB-C to mini DisplayPort adapters, using mini DisplayPort to DisplayPort cables. The screens would work, but with lots of issues, including:
- the mini 2018 could not remember which screen was which, causing it to apparently randomly switch at boot so that e.g. the horizontal display would be driven in vertical mode, or e.g. the secondary display would become the primary login screen
- there were lots of display issues including the screen intermittently blanking out and the display shearing along the bottom (which I didn't even think was possible for a digital display)
I don't know if it was the adapters, the cables, the fact that the cables are mDP to DP and not just straight mDP, a lack of support for mDP in general, or issues when connecting the adapters to the same Thunderbolt 3 bus.
Basically for the time being I wouldn't try using Mini DisplayPort with the Mac mini 2018.
And I will note that I saw similar issues with two Mini DisplayPort to DisplayPort cables directly connected to a Mac mini 2014's Thunderbolt 2 ports when running macOS Mojave (10.14).
HDMI Issues
Using the built-in HDMI port, the Mac mini 2018 will drive 4096-by-2160 resolution at 60Hz but only if you have a monitor that supports HDMI 2.0.
On the Dell P2415Q for example, you have to disable the default HDMI 1.4 support in order to enable HDMI 2.0.
I also found that the mini 2018 could not drive HDMI through an HDMI switch, specifically a Yunzuo 4x1 HDMI Switch. The screen would constantly cycle on and off. I have not had this issue with using HDMI on any other computer. Possibly an HDMI version issue with the switch?
Previously
January 07, 2018 - 1920x1080 Full HD monitors and 3840x2160 Ultra HD monitors
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