This had me stumped. I was running Media Composer on my iMac with the Mojave OS. Updated to Big Sur and then installed Media Composer 2021.12. I test-ran this a couple of times - all OK (no hardware attached). When I launched today, it hung on reading the user settings. Uninstall/reinstall/trash MCState and all profiles etc. Multiple Force Quits. I had a BMD Ultrastudio 4K connected. Lightbulb moment - unplugged it - back to normal. I then uninstalled and reinstalled a new version of the BMD Desktop Video drivers and now things are up and running. I can't see a direct connection between the Avid User profiles and the hardware but who knows? Maybe this will help somebody.

Media Composer is a very large app with millions of lines of code. Many thanks for posting!

First of all, please allow me to express the fact that your last name, if it's really your last name, is the absolute best last name in history.

Second, thank you for this.  I was going nuts in the same way you were.  This worked 100%.  MUCH appreciated!

Paul

Tha's my name! Check my website: www.avid-companion.co.uk.