No HDMI signal after update

I also called them few weeks ago, they told me that the problem was probably comming from my external monitor and that I should contact acer to ask if their planning to release a new driver to solve the issue.

I'm an computer scientist myself I knew it was total bull***t but I also knew the person that was speaking to me could not do any better. So I told her that I would not do that but if she could just let my issue open. I think that if we are many to have this issue and to complain about it, it might become a priority to them.

This issue started right after install, I was able to connect to a 1080p tv via hdmi. I could then switch the cable to my 4K monitor and it worked as long as I did not shut down the computer (sleep was fine, it would wake up and continue to work). If I shut down I’d have to repeat the tv connection & then switch. Now nothing works. I think something is cooked regardless what their diagnostics say...

That's interesting as I was under the impression that the Catalina update also did a firmware update which prevented going back to Mojave. I wonder why the usb installation was successful and the other two attempts were not?

I'm still having problems with my mac mini but not as bad as others. Mine will only recognize the HDMI if I unplug my second monitor before boot up. Once its up and running I can then plug in my second monitor, usb c to vga, and everything works fine. If I leave the second monitor plugged in when I boot up it doesn't recognize the HDMI. So not the end of the world for me, I just have to keep unplugging and then plugging in the second monitor. Hopefully Apple will come up with a permanent fix soon.

I have had the same issue trying to connect a relatively old Sony Bravia TV through HDMI, was not detected by the MacBook Pro.

Found a fix though!

Ended up on this YouTube video: https://m.youtube.com/watch?v=8YwJ7xdSUAc

The guys goes to System Preferences -> Monitor and presses the alt key to force the detection of the TV and/or display the « Detect displays » button.

Hope this may help some of you!

I've upgraded to 10.15.2 and firmware now on 2.16 but if I boot up with my second monitor connected via usb c it still doesn't recognise my monitor connected to HDMI. I have to unplug the usb c connected monitor to force it to see the HDMI monitor and then plug in the usb c once its booted up. Everything then works fine. So not a solution for me unfortunately.

Fingers crossed they will eventually fix it.

I had the same issue with no signal from my Mac mini to my external monitor. I found and turned off screen time in system preferences and that resolved my signal issue.

Same thing. After connecting my mac mini to a low res TV and reconnecting it to a LG 4K everything is fine but when I wake up my mac mini again I see the same black screen.

Of course you shouldn't need to, but you could try a usb-c to VGA adapter.

And that’s a COMPLETE waste. If you read the thread you’ll see Apple knows about the issue, and it a firmware fix which is forthcoming...

Yeah it would appear that updating to Catalina resulted in some firmware change but rolling back the software does nothing for the firmware change.

And if you power it all down and do a restart, does it still work?

Just wait until it goes to sleep.

Same problem here with my Mac mini 2018.

Just upgraded to Catalina, now same problems with HDMI connection to my 4k Samsung display.

Lower resolution displays work fine even connecting via HDMI.

No problems with Mojave before.

yep, same issue here

I own a 4K Samsung monitor.

I had to fight to make the OS starting after the Catalina update.

Now OS starts correctly but the start screen is pink color instead of the default black

I just chatted with Apple Support, and they organised a callback from their Senior Support team tomorrow evening. They did not have the issue listed on their system, but I gave them a link to this discussion, and we will take it from there...