Ok, after a little more messing around, I have been able to replicate what I did a year ago to solve this, and for me the problem is resolved again after my factory reset. The issue seems to be a problem with the panel self refresh system.
First, make sure you are up to date with Windows Update, then download the latest display drivers directly from intel at:
https://www.intel.com/content/www/us/en/download/785597/intel-arc-iris-xe-graphics-windows.html
Launch the installer package executable, when the installer loads, accept terms, decline improvement program, customize install and uncheck ARC control and Driver Support Assistant as you don't need them. Install the graphics driver and restart.
Once restarted launch the Intel Graphics Command Centre and we are going to disable variable and self refresh technology, so change the following:
Connected Displays (second icon down) go to global settings and disable Adaptive Sync
Next Go to System (fourth icon down) then Power, disable Panel Self Refresh.
Restart.
Now hopefully you should have a system that is much smoother when scrolling and free of the display tearing and glitching that ruins the experience. You may be able to just disable panel self refresh, but I did not notice anything not working after disabling Adaptive Sync.
It may also be possible to simply download Intel Graphics Command centre from the Windows Store, but I did not see the option for toggling panel self refresh in the factory driver.
Hope this fixes your machine too.
Rob.