Since upgrading to MacOS Ventura (13.1), there have been issues with connecting my Samsung C49RG9 Ultra-Wide to my MacBook Pro.

After connecting via a USB-C <-> DisplayPort cable the output on both the external and the built-in display would appear completely mangled into nice little colorful snippets. Similar issues appeared when using other cables / connection setups.

There is a workaround, the following dance has to be performed:

  1. Unplug the external monitor from the laptop
  2. Execute sudo sleep 20; sudo kill -9 $(pgrep WindowServer). This kills the window server after a delay.
  3. Quickly plug the external monitor back in while the delay has not yet passed.
  4. The window server is killed and will be restarted. Both the external and built-in display should work as expected.

Credit: I orginally found this workaround here.