Thanks for your thoughts but I get exactly the same behaviour across three different devices - it’s not confined to that one PC. That desktop has a Quadro P2000 graphics card. The two laptops are i5 and i7, both with integrated graphics. The problem was so bad on the i5 laptop that I uninstalled Norton - a solution that I may soon end up with on the other PCs unfortunately.
The only common factor between the PCs (apart from me) is that they’re all still running W10.
My screenshot showed nearly 50% utilization for Norton - if that’s not unusual then it’s definitely getting uninstalled!
But the key thing is that CPU utilisation drops dramatically and the cursor problem disappears as soon as Norton is open on the desktop rather than just in the system tray.
I think that my trust level must have just changed, which is helpful.