USB C ports not working for external monitor since installing Ventura 13

Hello Stewart_,

You've taken some great steps to get your USB-C ports working as expected on your Mac. At this time, we suggest that you use Apple Diagnostics to test your Mac for a hardware issue:

"Prepare your Mac

1. Shut down your Mac.
2. Disconnect all external devices except keyboard, mouse, display, Ethernet connection (if applicable), and connection to AC power.
3. Make sure that your Mac is on a hard, flat, stable surface with good ventilation.

Start Apple Diagnostics

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Turn on your Mac and continue to press and hold the power button as your Mac starts up.
2. Release when you see the startup options window, which includes a gear icon labeled Options.
3. Press Command (⌘)-D on your keyboard.

Intel processor

1. Turn on your Mac, then immediately press and hold the D key on your keyboard as your Mac starts up. 
2. Release when you see a progress bar or you're asked to choose a language.

View the test results

Apple Diagnostics shows a progress bar while it's checking your Mac:

When testing is complete, Apple Diagnostics shows the results, including one or more reference codes. Learn about Apple Diagnostics reference codes.

To repeat the test, click “Run the test again” or press Command-R.

To restart your Mac, click Restart or press R.

To shut down, click Shut Down or press S. 

To get information about your service and support options, make sure that your Mac is connected to the internet, then click ”Get started” or press Command-G. Your Mac will restart to a webpage with more information. When you're done, choose Restart or Shut Down from the Apple menu."

If your Mac is experiencing a hardware issue, we suggest that you reach out to Apple directly. You can connect with them by following this link: Get Support

Best wishes!

"Tell us what's on your mind", it says just before I clink the "Reply" button. Well then here's what's on my mind. I think the average "Community Specialist" quite often oversteps their level of competence. To be very specifically clear in this particular case, the OP has stated things were working before installing MacOS Ventura. But the "Community Specialist" suggests taking steps that have NOTHING WHATSOEVER to do with the problem unless the "Community Specialist" believes MacOS Ventura damaged the OP's hardware. There, I've said my piece and it's the largely the reason I don't come here when I've got a problem that doesn't already have an answer someplace else.