MacOS 13.4 Ventura - External Monitor no longer detected. Worked until the update to 13.4

This may well explain it. Some docks require third party software DisplayLink in order to support displays. Maybe this needs to be updated.

Thanks Luis. I re-installed DisplayLink driver and it worked for me as well.

Yep worked for me too. Thank you thank you. Pulled the monitor plug out from powerpoint and disconnected USB-C from computer for over a minute, plugged back in and works.

In System Settings->Desktop & Dock, under Mission Control, make sure that “Displays have separate Spaces” is CHECKED. Logout and login again to activate this feature, and the problem should be solved.

Have you tried using your monitor on another device? I tested it today and it looks like the DisplayPort input stopped working. I did the following test: I bought a new cable (usb c / displayport) and connected it to the monitor that had a problem, it still didn't work. It couldn't possibly be the cable, because the cable is new. So I decided to get the new cable and connect it to my other monitor (they are two identical monitors) and it worked correctly on displayport, so the problem is the monitor. Somehow the DisplayPort input on my monitor 2 has stopped working for no apparent reason.

Same problem after updating to Ventura 13.4.1

Connected my monitor over USB-C and after the update the monitor is visible in Display settings but no external screen output. Monitor stays dark and goes to standby.

Got it working after reboot, unplugging/replugging, and unplugging ALL devices from AC.

Often i wish i could roll back the updates.

Thanks for the super speedy reply. I persevered using every permutation of cable and order of connection. Bizarrely, the MBP detected there was an external display connected when I used an HDMI cable when both the hub and the monitor weren’t powered!

It showed a second monitor in ‘settings > displays’, but the name of the monitor showed as seemingly random characters (not the model number). I connected power to the monitor, which then worked (and report the correct model number in settings).

Finally, I switched back to the Display Port cables, which now work fine again 🤷🏻. Took two hours in all.

Okay, so i just re-installed the driver for the pluh\gable dongle and both monitors came back...all 3 screens working as usual.

The solution is actually simple. Plug the Macbook as usual to the screen. Unplug and plug the energy cable of the screen. It worked for me!

changing cable from 8k30hz to 8k60hz which has 32gbps speed solved the issue when m2 air didn't work with hp34'

My HP has an option of power efficiency in menu. Turned it off and it works fine now. Try to find the same option if your monitor has it

So I have been having some trouble too because until the update I was able to connect my M1 MacBook Pro to 3 displays. But now Apple's website reads that you can only have one extra display:Connect one or more external displays with your Mac - Apple Support

"You can connect one or more external displays, depending on your Mac.

• For Mac computers with the Apple M1 Chip: You can connect a single external display to your Mac. Docks don’t increase the number of displays you can connect. On a Mac mini with M1 chip, you can connect a second display to the HDMI port. See the Apple Support article Mac computers with Apple silicon."

So that may be a contributing factor as well like it is for me. I hope it goes back to the way it was!

Again: reinstalling DisplayLink has worked for many.