Mac Mini M4 no longer connecting to 3 displays

The signals used to drive displays, often at speeds in excess of 20 G bits/sec, are operating very close to their maximum switching speeds for this type of digital logic. cable length is also very important.

One common issue users are encountering is that more recent versions of MacOS are even less tolerant of transmit errors caused by cables that are not quite good enough to do this job, or are slightly too long.

If a cable connection incurs an error, the display affected can drop out.

Troubleshooting involves looking up exact parameters of the display, and making certain the cables you are using are certified for this use.

If you would like Readers to provide an analysis, please provide make&model of each of your displays.

Well I found my answer. The TV was alluding to it all the time. Not sure why I could not do this from system settings. Feels a little like windows (Sorry)! But had to go into system settings and at the mirroring option to the Menu bar. Then clicked on that and the 4K TV showed up and I was able to tell the computer that I want it as an Extended Display. I feel I should have been able to do this from the display menu. or the display menu should have showed the 4K TV and asked me what to do with it. This is sloppy by Apple. Just Sloppy software.

"Mac Mini M4 no longer connecting to 3 displays: This used to work fine before upgrading to Tahoe OS.[...]It will only recognize 2 of the 3 displays. If I unplug one of the monitors, it will display on the 1080p tablet and the connected monitor, but as soon as I plug the monitor cable back into the thunderbolt port, the 1080p display freezes, displaying what it had been displaying. If I unplug the 1080p's HDMI cable from the mac, and plug it back it, the 1080p screen just stays dark.[...]"

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Mac Not Seeing Screens After Update:



Verify the Connection:

First off, see if the displays are even seen: 

1. Hold Down: the Option key
2. Click: the Apple menu
3. Choose: System Information
4. Expand: Hardware
5. Select: Graphics/Displays from the list on the left
6. Look For: all of these items

Well I found my answer. The TV was alluding to it all the time. Not sure why I could not do this from system settings. Feels a little like windows (Sorry)! But had to go into system settings and at the mirroring option to the Menu bar. Then clicked on that and the 4K TV showed up and I was able to tell the computer that I want it as an Extended Display. I feel I should have been able to do this from the display menu. or the display menu should have showed the 4K TV and asked me what to do with it. This is sloppy by Apple. Just Sloppy software.

"Mac Mini M4 no longer connecting to 3 displays: [...]This used to work fine before upgrading to Tahoe OS.

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Mac Not Seeing Screens After Update:

Report this to Apple:

Do your Part: Inform Apple of your feedback of this issue. Include how you’ve troubleshot this, and your results. Apple wont get back to you directly, but the more feedback they receive from its users, the more they will know what issues are occurring, and what bug fixes to include in updates to come. Apple with know nothing of this occurrence, if you don't report it to them.

1. Go Here: Feedback - macOS - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Select: "Software/Firmware Update" for the "Feedback Area"
4. Comment: the this all started after upgrading to macOS Tahoe. Include the URL of this thread.
5. Proceed from there as necessary

LG 27UK500 appears to be a 4K UHD resolution of 3840 x 2160. capable of 60 Hz refresh

it is capable of 10 bits/color HDR=ON (by using FRC dithering for the last two bits.)

connections include

2x HDMI 2.0

1x DisplayPort 1.4

to run that display using 10 bits/color HDR=ON HDMI from a Mac ThunderBolt port, the adapter/cable must be certified as PREMIUM high speed, capable of that speed and refresh rate. The timings will be modified to 4:2:2 bits /color chroma subsampling to achieve 60 Hz. Anything higher would require more data than a thunderbolt port can support.

at 8 bits/color HDR=OFF, 60 Hz is achievable without that chroma subsampling.

for DisplayPort, at 10 bits/color, 75 Hz would be directly achievable, PROVIDED the display supported that (it does not) and the cable length was limited to ONE meter maximum. 8 bits/color could support up to 120 Hz, if the display could support it, again provided that the cable was ONE meter or shorter.

I am having the same issue. 2 27" Acer Fire Legend monitors connected to USB C at the rear of the computer and a 43" TV connected in the HDMI port. It literally worked yesterday no problem. I did experience 2 of the monitors going black then coming back on yesterday. But they worked. I put the computer to sleep and woke it up this morning and only 2 Monitors. The TV just sits and says "Choose to Mirror or Extend Display from the (Has a display iCon I think) menu" When i unplug any one of the two working monitors the TV works. Just happened all of a sudden and I have done nothing really. I did upgrade to 26.1 but all monitors were working after that. Come on Apple I wish it just worked like Apple Computers use to.

Just to add the system does see it as a HDMI audio source.

what I can find immediately is those displays are not wider than 2560 wide.

To reliably use those two displays with adapters, the USB portion of that cable must be no longer than One meter.

The specs required for modest resolution HDMI displays is shown in an earlier response.

Let readers know you are using cables that meet those specs.