Hi everybody,
A week ago I updated my Mac to Catalina, and my audio interface is the Mbox 3 Pro.
To be honest everything work just fine, no issues at all so far.
So, if you have the Mbox 3 Pro and thinking of updating the Mac to Catalina, do a backup and give it a go! It should be working, and if it doesn't you can simply use Time Machine.
Again, I'm working right now on my PT HD 2019, iMac 2017, Catalina 10.15.3 using Avid Mbox 3 Pro... All good!