I have solved the issue. In Cubase 12 ARO loaded with a red exclamation mark in the top right. This is typical when you try to use a purely Native plugin (so not Intel compatible) in a DAW running in Rosetta mode. This happened despite the fact that Cubase 12 did not show a tick under Open using Rosetta in the Get info tab in the Applications folder.
So I ticked Open in Rosetta. Started up Cubase 12, closed it again and took away the tick and started again and “Oh wonder”. Firstly I got a lot of messages from the Plugin Manager on none compatible VST3 plugins and when I loaded up an ARO track it worked correctly
So for some reason Cubase 12 ran since I installed it using Rosetta without showing a tick in the Application folder.
For those interested in the folders in the root directory of my MBP. Here a screenshot
The other VST3 outside the Plug-Ins folder is empty. The VST2 folder as well.