The diagonal thing, didn't solve the problem. It might have helped, but that might have just been wishing.
This actually seems to work (12 hours ...)
https://www.laurivan.com/fix-crazyjumping-cursor-on-a-macbook-pro/
Go to System Preferences > Accessibility > Mouse & Trackpad
Check “Ignore built-in trackpad if external mouse is present”
Play around for a bit with your mouse, say 15 seconds
Come back to the preferences tab and uncheck that box.
Commenters say they used USB mice, I've got a wireless mouse (did it with or without, did it different wireless mice)
I've had this problem since I first received my new MacBook Pro two weeks ago. I'd been searching for overly sensitive track pad. Yesterday I searched for MBP cursor jumping all over the place I found threads leading to this tip. One commenter said he received this fix from the Genius Bar