The install of MacOS Sonoma went okay and things seemed fine after installing the OpenCore root patches. Strangely, Arc took anywhere from 30 - 60 seconds to start and appeared to be the only app that had any trouble.
Not good.
I tried removing and reinstalling and even a new Mac user account but got the same behaviour.
Seeing as it's where I spent the most time on my Mac I have decided to revert to Ventura. The partition has been wiped and I'm reinstalling.
@colinwalker appreciate the update! As a fan of Arc, I'll hold off for now - thanks for the tip!
It's most likely OpenCore Patcher causing the issues rather than Sonoma itself.