No HDMI signal after update

Resetting PRAM & SMC took a 3 (4K monitor) setup with the HDMI port not working at all (meaning only 2 monitors working), to a 3 monitor setup working with all 3 monitors running at full 4K resolution at 60hz. Of note the PRAM reset lead to the HDMI working at 1080p but not 4K, then the SMC reset took the HDMI port to 4K 60hz!!!

I tried Ctrl+Command+alt+Shift+R before startup apple logo, it worked (TCL 4k), but only at the second or third try.

First it recognize the screen 2160@30hz, then it switched to 60hz at login screen.

A temporary fix. After trying everything I could think of with monitor settings/cables/changing settings through remote display... I found some help on another forum from someone who called support.

To summarize the issue: Mac mini - HDMI to HDM connection to a 4K display (many users with lower-res displays chiming in do not appear to have the HDMI issue). -- Another fix is to buy a USB-C to HDMI or Displayport adapter (if your monitor supports).

Temporary (I hope) Fix: Appears to be a SMC issue. Shut down the mini. Unplug for 5 seconds. Plug back in and hit power. This seems to fix the HDMI signal for a period. But it doesn't hold after display sleeps for a longer period. Hope this helps. Apple really released a buggy OS this go-around. Disappointing and I hope they get this fixed.

After Catalina update on my 2018 Mac Mini, the HDMI signal to my Sony 4K bravia failed (no issues before the update). After reading through this post I decided to get Apple Support involved (misery loves company). After 2 hours of attempting everything shy of connecting another monitor (which I don't have), I requested a visit to my local Apple Service Center. Predictably, they could not duplicate the issue using a USB-C-to-DVI cable. I informed them that the issue was with HDMI video, to which they had to buy a cable to troubleshoot with - UGH! They still didn't fully understand the HDMI configuration that many on this forum are using - HDMI-to-HDMI 4K monitors (UHD TVs or otherwise) and still could not duplicate the issue. So, I bit the bullet and bought Apple's $69 USB-C Digital AV Multiport Adapter. Connected BOTH HDMI and USB-C/HDMI from the mini to separate HDMI inputs on the TV. When powered on with HDMI source selected, no signal. Changed source to USB-C/HDMI - WOW! got video. Now the test: switched BACK to HDMI-direct - signal remained! However, when cycling TV power, I have to repeat the source-switching dance to regain the 4K 60hz HDMI signal (research indicated the Multiport Adapter output is only 30hz). I have reported my findings back to Apple Support and hope this helps them and many of you.

Adapters don't solve the issue with a 3 monitor setup. It appears no matter what you only get 2 monitors working on USB-C and one on HDMI.

Unless someone has a combo working with 3 USB-C ports, let me know.

An odd development, yesterday I could not get my HDMI monitor to work at all. Unplugging, reboot, etc., none of the usual tricks worked. then I decided to try my monitor on another machine like I’ve done countless times.

I plugged my hdmi cable into an old MacBook Pro, the monitor worked as usual. But then I plugged it into the mini and it came on.

no idea why, but plugging my monitor into another machine, then back in the mini fixed it this time. Doesn’t make much sense, but maybe it will help someone else out until Apple fixes this.

Note that this issue occurs with 3rd party hardware as well. My MBP uses a OWC USBc Dock when it is at my desk. Catalina update (including the .1 release overnight) has resulted in the HDMI-port of the dock only holding a "synch" with an external monitor for about 10 seconds, and then blue screening.

Plugging the same screen in via a USBC-HDMI adapter and it works fine.

I'm expecting a cloud to open and sunrays to shine through ... or a lightning bolt will hit me ... but ...

Since installing the macOS 10.15.1 update on my system this morning, I can now run my monitor with only the HDMI cable and port AND I can shut the power off! I've done it several times, and not only does it work, but it gives me back the highest 3840 x 2160 resolution I wasn't getting from the USB-C to HDMI Adapter (best was 3200 x 1800 with it).

Please someone else try this and let me know it really works as I may be dreaming ...

Update: The last time I not only did a "Shut Down", but I pulled the power cable on my mini and waited about a minute. Plugged it back in and it started right up -- my Mac mini 2018 and Toshiba UHD TV/Monitor now powers up and displays 4K via only the HDMI port and cable.

No luck here. Release notes for 10.15.1 didn't mention anything about a fix and people replying earlier using the beta version of 10.15.1 said it wouldn't address this issue. I was hoping they were wrong, but it looks like they were correct. Still no fix.

So sad that apple cannot handle his self-built current hardware with his current OS. I don‘t think it‘s exotic to connect a 4K-monitor through a built-in-hdmi-connector. So sad...

I want my current mac to get a current os.

I had the same good luck with the 10.15.1 update

after updated rebooted (power down ) and the after everything settled down . Power down and hook directly to the HDMI port and powered up.

display came up right away 4K hdr 60 hz to my lg 4K monitor via HDMI .

seems 10.15.1 addresses the issue

Since I also reported success with the 10.15.1 update, I'll reply that my machine goes to sleep regularly and I have no problem 'waking' it, I continue to get a 4K output to my monitor with only the HDMI cable connected (I've removed the USB-C to HDMI adapter from my system). As reported previously I can also power down, and even unplug my mini and it still works.

However I'm sorry to hear that the 10.15.1 update isn't solving this problem for everyone, and we can't say what percentage it does fix as we only know who comes back to report here.

It certainly would be interesting to know what differentiates the monitors that still don't work, vs those that work with 10.15.1, vs possibly some that continued to work through the 10.15 upgrade (and never even knew there was a problem).

The HDMI issue on my 2018 Mac Mini using a 4K TV as a monitor was fixed with 10,15.1. After the update, I unplugged power to both the Mac and PC. When both powered on, HDMI 4K / 60 HZ worked fine, and has survived many power on/off cycles.

It does seem that the 10.15.1 update may have fixed the issue. Like others, I did also need to do the whole power off and unplug routine, and one time it still came back from sleep with the resolution messed up, but after a subsequent restart it’s running normally through my direct HDMI connection, and returns from sleep normally.

I’ll report back if I notice anything odd but this is encouraging.

Is there a solution - after upgrade no longer does HDMI work with Catalina - SMH that Apple did not check this given their resources or issue some notice as to "what's new" and "what you have to do to fix the HDMI connection"