2018 Mac Mini - monitor problems

I've got a 2018 Mac mini. After having installed Catalina 10.15.2 all my problems seemed to be solved. HOWEVER, after updating to Catalina 10.15.3 all problems back again. External monitor twinkles, flashes... so back to usb-c Hdmi cable.

It a shame Apple does not take into account our complaints

I'm on 10.14.6 and thought the problem was resolved (for me) but it's back. Using USB-C to DisplayPort. I agree with cpmax that it's with 60 Hz.

Also just discovered that my Thunderbolt 3 drive gets disconnected when I turn bluetooth on...

Same problem here and no reliable fix after weeks. In case this helps, Apple won't look at this thread but hopefully take into account our feedbacks from that point: https://feedbackassistant.apple.com/

I have added mine.

I am having similar problems with an old 1080p NEC EA231WMi connected via HDMI to DVI. The monitor worked initially when I bought the Mini (in 2018) but for months it has refused to display anything on power-up. Occasionally it works if I unplug and plug the video cable, but often I can monkey with that for 20 minutes and get nowhere. If I type my FileVault password blind and get the OS to boot, the display comes to life.

I would try it now without the adapter and see if it's still working.

My humble experience was using an old Apple adapter that was barely 4K (30 Hz or some such), loads of flicker and really bad - but after I tried it, everything worked whether I did straight HDMI or USB3-to-DisplayPort.

It still works. I am, though, afraid to use Catalina! Though I don't want to anyway because I like my old Adobe and Microsoft apps and have no desire to pay hundreds of dollars a year for worthless “upgrades.”

I had the same problem with 4K monitor. Was very frustrating. I tried your solution and worked perfectly first time. I think you're right, something is preventing the video card from working, I guess no encryption for me.

PerChristensen, nickstock is saying that an upcoming release of Catalina, 10.15.4 not 10.15.3 which is what is available today, fixes the issue.

Oh wait, I see now you were replying to Davert. Sorry about that!

If you haven't opened up a support ticket for this issue I recommend you do so. Even if you are past warranty and don't have Apple Care. After several months of troubleshooting with them we came to a resolution (not a fix). I can't go into details for my case here as your situation might be different but if you don't open up a ticket you won't know what options are available to you. I'm very happy with the option they offered me.

Good luck everyone!

I'm on 14.6 and what fixed it for me was not software, it was confusing the video stuff by using a crappy 30 Hz HDMI adapter. The video system must have some sort of PRAM of its own which is not reset by PRAM updates and such.

A temporary fix for me was restarting PRAM every time I booted. Wasn't a real fix.

My system is now OK which just astonishes me. It does not look as good with HDMI as with DisplayPort but displays the same resolutions and refresh rates on both.

I was perturbed to read this thread when I was waiting for my monitor to arrive because I had ordered an LG 27UL850-W but I was pleased to find it works well with my Mac mini 2018 using the provided USB-C cable. The default display setting was 1920x1080. It took me a while to find the other resolutions under System Preferences. I'm using Catalina 10.15.4.

I suspect this might not help those with older monitors from what I read before but I thought I would post about an LG monitor that works with the Mac mini 2018.

I believe the issue is with HDMI versions below 2.0, and maybe DisplayPort. That said, Apple should have fixed it anyway. And I probably should have returned my Mac when it wouldn't work well with my monitor rather than trusting Apple to fix it.

(I am doing OK with the monitor now, for the most part, but having issues with shutdown-from-sleep since the last update, and using Bluetooth kicks off the Thunderbolt 3 drive.)

The issue is that for some people (me) this calling resolution option is not available when I connect my 4K monitor to the mac directory using the DHMI port. However, for some reason, this option IS available if I use a DisplayPort to HDMI connector and connect the monitor via the DHMI cable to the display port. I know that the DHMI port hardware can correctly use 4K as the initial firmware boot screen is in 4K, but once the mac OS starts it switches to 1080. The System Preferences -> Displays still correctly identifies the name of the display, but the higher resolution options aren't shown in the drop down list. If I use the HDMI to DisplayPort adapter, the boot screen is in 4K, and once the mac OS starts it stays in 4K. When looking at System Preferences -> Displays it shows the same name of the monitor, but this time there's a bunch more resolution options available in the drop down list.

Conclusion.s:

1) The HDMI hardware port supports 4K, as witnessed during initial firmware boot screen.

2) The Mac OS supports 4K, as witnessed when using DisplayPort to HDMI adapter.

3) The Mac OS has buggy support of 4K via the HDMI port. <<< This is what we all seem to be complaining about.

See https://newall.ca/mac_mini_monitor_problems/

If you want to wipe the drive and do a clean OS install from a thumb drive, you need to set your machine to allow external boot.

You can Google how to make a bootable usb installer. Here’s the step to allow booting from an external drive.

https://support.apple.com/en-us/HT208330

Same problem intermittently with my 30” Cinema Display. Attached by USB-c to Mini DisplayPort adapter to dual-link DVI adapter. Reboot x1 always works.

As far as I can tell, wait for 10.14.6...