How to turn off smooth scrolling for apps and start menu in Windows 10?
You're in fact asking two different things. I can answer the title question.
One option is called Smooth-scroll list boxes and it is located in
Control panel > System > Advanced system settings > tab Advanced > Performance
Tick it off and list boxes (like Windows Explorer with lot of files) will react quickly to mouse wheel. There's no need to restart / log off.
Another option that may apply to your problem is Animate controls and element inside windows. Anyway, try to fiddle with these options and then please leave comments below.
(Tested with Windows 7)