Adjusting the backlight makes no difference - nor does anything else I have found by searching on forums.
I have had extensive chats with Microsoft agents. The last one was able to see the problem himself while we were connected via a logmein session. He suggested that the wall sockets in my home might be the source of
the problem, perhaps overpowered - but we laid that excuse to rest by drawing the mains power from my battery-powered uninterruptible power supply - which will have been producing a very clean and regulated power. The cursor sticking problem remained. He also
had a good look through all my software, drivers and power settings and could find nothing amiss.
Just is case it might be my fingers, I have had my partner also try the Surface Pro - but the result is the same.
I am returning this Surface Pro 7 and will test another, in case it is just that I have been supplied from a batch with a manufacturing fault. I have spoken with two friends who have Surface Pro 5s. They tell me they do not experience this problem.
At this point I have tried two different Surface Pro 7s, three different power chargers, and three different Signature Type Covers. All exhibit this very frustrating problem that the touchpad cursor sticks and freezes when the computer is running on mains
powered.