I can confirm very slow Plasma responsiveness and jittery cursor with a GeForce GT 710 on a very fast machine, with both the recent short- and long-term Nvidia drivers. It doesn’t matter what the resolution is or what the refresh rate is set at, the Application Launcher menu, for example, takes 1-2 seconds to pop up, and I have all desktop effects off!
Firefox, however, renders fast, but menus etc. pop up just as slowly.
And Plasma with the VESA driver is fast.
It’s some combination of Plasma with the Nvidia drivers that seems to be causing the slowdown.
The tricks mentioned in this thread don’t help.
I’m using KDE Plasma 5.14.4.