I appear to have fixed this.
I deleted the videoengine.dll (from - C:\Program Files\Steinberg\Cubase 12\Components) and it was then freezing at ‘initializing chord pads’. Nothing that I was doing seemed to get it past that point.
I tried disabling and deleting the preferences multiple times, but it would always freeze at the same point.
Finally, what fixed it: I navigated to the appdata folder for Cubase 12 (C:\Users\DAW\AppData\Roaming\Steinberg), deleted the Cubase 12 preferences folder, and then re-enabled my old Cubase 11 preferences folder (which I had renamed ‘Cubase 11_64_old’).
I removed the ‘_old’ and tried again, and suddenly Cubase 12 decided to load successfully.
It did not load the first time that I attempted to run Cubase 12 with my Cubase 11 preferences enabled, but is working now.
It seems weird to me that stuff like this was not picked up in beta testing. Maybe they need to cast a wider net to avoid stuff like this.