M4 Mac mini stopped supporting dual monitors

Question

M4 Mac mini stopped supporting dual monitors

This is the strangest situation I have ever come across. My M4 Mac mini stopped supporting dual monitors. Dual-Monitors used to work, and now it doesn't. Follow me on this, it is the strangest thing you will read today I'm sure.

My setup
M4 Mac Mini, 24 GB.
OS: macOS Tahoe v 26.0.1.
Primary Monitor: Dell 49" Ultra-Wide, 5120x1440 @ 60Hz, Connected by USB-C / Thunderbolt 4.
Secondary Monitor: Dell 28" 1920x1440 @ 60 Hz., Connected via HDMI.

When I boot with either Monitor alone, they work. No hardware problems of any kind.

When I boot with both monitors, the secondary HDMI monitor shows the Apple Logo, and my Primary monitor shows the boot-up status bar, until I can login and use the computer as usual.

The secondary HDMI monitor however, goes blank. It remains powered-on and the wallpaper displays, but no icons or anything else.

In Settings / Displays, NO SECOND MONITOR is visible. Pressiing OPTION and trying "Detect Displays" does not show the other monitor.

Thinking that the HDMI port may have become damaged or something, I tried connecting another USB-C / Thunderbolt monitor and the exact same behavior occurs.

So of course, this looks like a software glitch, right? I even tried re-installing the OS from a Time machine backup. Apple support told me to take it to the Apple store but the guy that tried to help me couldn't figure it out either.

Any ideas what the problem could be, community?

Thanks in advance!

Mac mini, macOS 15.6

Posted on Oct 8, 2025 7:38 PM

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Answer 1

Top-ranking reply

nuevakenia

Level 1

24 points

Oct 9, 2025 10:37 AM in response to Mark from 2Much

i fixed a similar issue with a macbook pro 2021 m1 16" with 2 external screen, allowing only 1 active.

# Remove global WindowServer preferences
sudo rm -f /Library/Preferences/com.apple.windowserver*.plist

# Remove WindowServer cache/database
sudo rm -rf /private/var/db/WindowServer

# Remove user-specific display profiles
rm -f ~/Library/Preferences/ByHost/com.apple.windowserver.displays*.plist 2>/dev/null

# Remove ColorSync profiles linked to displays
sudo rm -rf ~/Library/ColorSync/Profiles/ByHost
sudo rm -rf /Library/ColorSync/Profiles/Displays 2>/dev/null

# Restart display services (this will log you out)
sudo killall -HUP WindowServer

this kill your desktop for a seconds and erase the desktop arrange, fixing it for me.

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Answer 2

Oct 8, 2025 8:24 PM in response to Mark from 2Much

Not sure this will help given the HDMI display does work on it's own, but macOS has become progressively less tolerant of video data packet loss due to sub-par cables. There have been several reports of setups that worked in Sequoia not working in Tahoe, with nothing changed but macOS.

Best recommendation at this point is to try a new cable. Be sure to use high quality cables – HDMI should be labeled Ultra or Premium, USB-C cables should be rated for high-speed data transfer, etc. Also, cables should be as short as possible (≤1 m for most cables, <0.5 m for Thunderbolt 5 cables). That random cable you found in a drawer might or might not work.

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Answer 3

Oct 9, 2025 7:33 AM in response to Mark from 2Much

Odd, indeed. Does it behave like that in Safe Mode?

Start up your Mac in safe mode - Apple Support

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Answer 4

Oct 9, 2025 10:06 AM in response to Mark from 2Much

Update: I just discovered something interesting.

If I enable screen sharing to my iPad, then the secondary monitor appears in Settings / Displays, and it works properly. If I disable screensharing or disable my iPad, then the secondary (HDMI) monitor disapears from Settings / Displays.

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Answer 5

Oct 9, 2025 10:35 AM in response to Mark from 2Much

UGH...

Here’s what I tried:

NVRAM / SMC reset
Safe Mode and new user profile
Removing display preference and override files
Re-enumerating WindowServer and display daemons
macOS reinstall and SwitchResX EDID reset

Nothing fixed it. Interestingly, the HDMI display appears only when I enable Screen Sharing as mentioned earlier, suggesting a WindowServer / display-agent enumeration bug.

According to ChatGPT, It is a known issue (Radar FB14182449) and it’s expected to be fixed in macOS 15.2, though it couldn't provide any links as proof.

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Answer 6

Oct 9, 2025 10:08 AM in response to Mark from 2Much

I have seen this workaround reported by others for single monitors, as well. Suggests the issue is a Tahoe bug.

Bugs can be reported to Apple here:

Feedback - macOS - Apple

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Answer 7

Oct 9, 2025 7:30 AM in response to neuroanatomist

Hi neuroanatomist,

Thanks for the reply but cables are definately not the problem. I tested with a variety of both HDMI and USB-C / Thunderbolt cables, and even with different monitors, and the exact same problem is there.

To clarify - when 2 monitors are connected, regardless of which monitors and which cables are used, the secondary monitor "works" in that it shows my background wallpaper on it. I can't mouse-over to it, I can't drop any icons to it, and Settings / Displays does not recognize that there is one connected.

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