External display not working after installing MacOs Catalina

I have a very similar setup, Late 2012 Mac Mini using a d2 Thunderbolt HD to daisy chain both a 27" Thunderbolt Display and 2012 27" LED Cinema Display and everything worked perfectly fine on High Sierra before I decided to update to Catalina. Now the problems I have are absolutely ridiculous:

1. If I disconnect the HD, my Thunderbolt display goes completely black and I have to force Shut Down my Mac Mini
2. If I restart, my LED Cinema Display doesn't turn on
3. Apps like TeamViewer no longer work which is extremely frustrating because we use it extensively for work

What does work:

1. Putting computer to sleep and waking still works fine
2. Starting screensaver and returning still works fine

Apple should've never allowed this update for 2012 Macs, it totally wreaked havoc on my machine and there is no recovering from it. I would've gone back to a previous backup but but the time I figured out that nothing was going to fix it a week had gone by and rolling back would've deleted a ton of work I had completed for work.

Not happy. Booooooooo Apple.

Come to think of it, I think I remember hearing something like this.

It seems very counterintuitive that the Cinema Display cannot be connected directly to the Thunderbolt Display's second port, but if you insert a hard drive between the two it works... so apparently you are forced to use this topology in order to have both displays working.

I have the exact same problem. Two monitors connected with thunderbolt to HDMI cables worked perfectly with Mojave but having upgraded to Catalina neither work straight away. They randomly come to life after about 30 minutes (often longer) and as soon as you disconnect and reconnect I have the same wait time all over again. “Detect displays” does nothing. Absolutely ridiculous for a very expensive MBP that I need to use at work and at home. I might have to go back to good old windows 🤣. Without any acknowledgement of the issue from Apple that I have seen I am getting a bit desperate because I can’t do my job with just the built in display. I read that using some sort of powered hub for indirect connection works. Anyone managed to do this?

This is absolutely a software/driver issue. Before Catalina everything was working fine. But the very first moment after the update, I had to leave the cable connected from minutes to hours till finally detects it. Sometimes after hours, I need to restart Mac, monitor, unplug and plug cables million times till it works.

After every new update, I cross my fingers that they gonna fix it with this one, but no!

I'm not going spent money on buying new cable because of the new buggy OS update! Really frustrated.

I'm sitting here reading your post as my two monitors have decided to go on hiatus this week and have to work solely off my laptop's screen (first world problem...I know). These are the cables I am currently using to connect my monitors to my laptop. Note they fit the specs that should work but don't (e.g. 60 Hz and supposedly are Thunderbolt 3 compatible) https://www.amazon.com/gp/product/B07KJHKHSF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

After reading cosmonaut507's post I ordered the two cables he recommended. This was not the first time these particular cables have been recommended for this problem. They are expected to arrive tomorrow before 9pm. I hope they work; but the description is almost exactly the same as the cables I ordered in May and referenced above. I will update this forum with the success/failure of my cable swapping at the end of the month...sooner if they just flat out don't make a difference. That should be enough time to vouch for the quality of this brand to solve the problem: https://www.amazon.com/gp/product/B075V5JK36/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

YAYYYY!!!!!!!! After a week of having both monitors out (or working very flaky at best) I connected both monitors using these cables and they both came up and actually look more stable than before. I say more stable as there has always been a "shakiness" to the picture quality that I've overlooked as long as they would function. I'll report back at the end of the month to let folks know if this was a definite fix or if there have been flaky days.

https://www.amazon.com/gp/product/B075V5JK36/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Just upgraded to Catalina and I lost my external monitor and mouse. They were both plugged into a usb-c (tried both on right side) via a SATECHI multi device adapter. On plugging it in, my USB power monitor also turns on for about a second and turns off. I suspect MACOS is turning the port off.

Although I did not look through every response, I did not see anything in this thread that worked or was helpful. I resolved the problem myself via the instructions in this link: https://support.displaylink.com/knowledgebase/articles/1916602-macos-catalina-10-15-screen-recording-permission

If someone posted this link I missed it.

Having the same issue, with a twist.

Monitor (DELL U2415) connected to MBP16 via HDMI port on HP Elite USB-C Hub (not the Dock that uses DisplayLink). This setup was working just fine with Catalina from day one, no issue at all.

Yesterday, I upgraded to Big Sur. Monitor is longer detected from that point forward. Tried NVRAM and SMC resets, monitor reset, the "detect display" button also. No change.

Now the twist: I rolled back to Catalina, and the monitor is STILL gone, can't get it back!

Monitor and cable continue to work fine when connected to a MBP2015 running Mojave, the last one with HDMI port.

I'm at a loss here. I mean, it was working fine on Catalina before, and Big Sur kills it without recovery after a rollback? ..... Just makes me want to throw this computer out of the window.

Hi,

More or less the same problem, but not exactly, after upgrading to Big Sur on my MacBook Pro 2016 16 GB.

External screen: LG Ultrfafine (sold by Apple)

Connection: the USB-C cable which does everything: video, sound, power.

Problem: when I detach the USB-C cable from my MacBook when it is on, and then attach it again, the MacBook will not recognize the display, also not when I press 'Search Displays' on the Displays System preferences panel.

After a restart however the external display is working fine.

Sorry about the delay. I bought the 2 cables, hooked them up and they both work with no issues. I hope this helps out.

I don’t understand what you are saying. If you are talking about a program called “Cleanmymac” then you are using one with terrible reputation and that ought to be considered malware. In any event, a third party program does NOT upgrade your mac to Catalina or any other version of the OS.

This is the program I am using. https://macpaw.com/cleanmymac I've used for over a year with no issues. It is not the one that would pop up on less reputable sites a few years ago. CleanMyMac X did not update my OS system. CleanMy Mac X updated to handle Catalina. If you were confused by my sentence in my reply, I apologize. I've had no problems with malware. I also run McAfee AV and no malware ever detected. I appreciate you looking out for us Mac users.

It’s your mac, your choice.

Cleanmymac is known to delete files that should be kept alone and to cause many problems, which often require a clean install of macOS to solve.

The most seasoned users around here also recommend against installing third party antivirus like macaffee, but again it’s your mac.

No. It does not. I had very little 3rd party software installed at that point other than OpenVPN and iTerm2. I had saw posts about that when I first tried to update and applied the permissions changes some of the other guides suggested. No difference.

Normally it "finds" the display within an hour, but it's around 3 hours today, which is why i'm here searching if there's any resolution paths yet :(