Hey, Michael!
Thanks for using the Apple Support Communities. From the information you provided, I'm gathering you've gone through the steps to updating the USB-C Multiport, but after completing the process it doesn't reflect on the system. I know it's important to make sure any updates get installed properly, and I'm happy to offer a few suggestions to help!
First, try installing the update in Safe Mode. The following article will guide you through booting into Safe Mode, and give you some more information what Safe Mode is.
Try safe mode if your Mac doesn‘t finish starting up
Even though the title of the article isn't directly related to your issue, Safe Mode is still a great step to take. It will run some checks on the system during boot, and will disable certain software that could be causing a conflict--so I'd recommend starting there.
If the update still doesn't install as expected in Safe Mode, you can also try to install the update in a new user account. The article linked below will give instructions on how to set up a new account, and gives an explanation of why this step might help.
How to test an issue in another user account on your Mac
Have a great day!