I used the main “Stereo Out” for this, but it seems the same on other channels.
Insert something that has stereo meters, e.g. Supervision or a stereo compressor.
Right click and select “Move to post-fader slot”.
Play audio, and pan to the left or right, the meters don’t reflect the panning.
Moving the fader up and down IS reflected, but not the panning.
Edit to add- Cubase 12.0.40 on a Mac.
This is normal, panning in Cubase is the last step before the signal is routed to the next bus in the signal chain.
If you want to apply effects post panner, route the track to a Group Track and insert your effects there. But if you want to keep it all in the same track (maybe for a creative effect or correction), use the VST MultiPanner or Imager in single band mode. For correcting a recording error, it might make sense to apply these effects via Direct Offline Processing instead.
Thank you for taking the time to reply and explain, much appreciated.
I think I get the reasons, and thanks for the workarounds.
I would suggest that on the master “Stereo Out”, the metering should show the reality as it’s the last reference point? If someone (a “friend” 
) accidentally left the pan pot off centre, and was watching the Supervision levels, it might give them a clue he’d messed up!
But, this obviously shouldn’t be listed as an issue.
Thanks again for your helpful reply.
EDIT to add, the Channel meter on the mixer does of course show any offset- so perhaps I’m trying to find a solution to a problem that doesn’t exist?!