Meanwhile, back in the lab … it was indeed the composition pipeline causing this behaviour.
I had to turn off Force Composition Pipeline in nvidia-settings for both of my dual displays to resolve this issue.
If even just one display has this setting, the ‘high % at low freq’ issue returns.
As requested, please find the nvidia-bug-report.log attached to Bug ID: 4341092 (I generated this before turning off the composition pipeline).
Note: not seeing any screen tearing with Force Composition Pipeline in nvidia-settings off. I see that Gnome 45 includes the latest mutter compositor. Been using Nvidia/Linux systems for a long time so forcing the composition pipeline on was just a (very) old habit.
Note: it would be nice of nvtop included kernel level GPU usage stats. I honestly thought I had some sort of crypto/AI malware infection when nvtop GPU process level stats reported no activity (0% usage - see above screenshot).
Thanks again.