Hi Stephen H,
In addition to the checks already suggested, I’d also rule out a connected device causing the pointer movement. Once the computer is usable again, temporarily disconnect any external mouse, wireless USB receiver, controller, drawing tablet or docking station. If it’s a laptop, you can also temporarily disable the touchpad and see whether the pointer continues moving.
Was the pointer simply drifting or did it appear to be deliberately selecting or opening items? Did the update screen show a percentage or spinning indicator and has the pointer moved by itself again since Windows restarted?
You can also search for View reliability history from the Start menu and check what was recorded around the time this happened, such as an update, hardware error, app failure or unexpected shutdown.
Please let me know what you find and I’ll be happy to help you narrow this down further.