External monitor pixelated after Ventura 13.2 update

Hi tolga_,

Thanks for posting in Apple Support Communities.

We understand that your external monitor shows pixelated and you have switched the HDMI cable. Since the Mac is working as it should, try connecting your display to a different computer to see if the behavior continues there. Check whether the monitor is damaged.

"Detect your display

If your Mac can't detect your display, your display will be dark. Use one or more of these steps to try again to detect your display.

• Disconnect the display from your Mac, then reconnect it. It might help to turn off the display first.
• Put your Mac to sleep, then wake it. On Mac laptop computers, you can close the lid for a few seconds, then open the lid again.
• Choose Apple menu  > System Settings (or System Preferences), then click Displays. Press and hold the Option key to show the Detect Displays button, then click the button.
• Restart your Mac. If you can't restart your Mac, press and hold its power button for about 10 seconds to turn it off. Then press and release the power button to turn it back on."

If your external display is dark or low resolution - Apple Support

Regards.

It's an issue with Ventura.

Open a terminal window and, without the external display plugged in, type

sudo sleep 20 ; sudo kill -9 $(pgrep WindowServer)

Then plug in your external display, wait a few seconds and it should work normally.

Hi tolga_,

You mentioned that it works well with other laptops. Are these other laptops running macOS Ventura as well? The reason we ask is that will help isolate this issue to the macOS. It's possible that your external monitor is not compatible with macOS Ventura or needs a firmware update.

We'd recommend confirming with the manufacturer.

Have a good one!

Did you try turning off mirroring?

Usually, you can do it with Command-F1 (or Command-fn-F1, depending on the settings); if your mac has a touch bar, press and hold Command and fn and tap the decrease screen brightness sign.

I am having the same issue as well. It was working fine until I upgraded MacOS to Ventura.

MacBook display is working fine until I connect it to the external monitor (Samsung CRG9), then both macbook and monitor display are pixelated. Also, tried mirroring, extending the display, rebooting macbook and monitor, but nothing is working.