I have two machines -- one using the nVidia drivers (396.24) and one not. Both use xorg 1.20. When selecting "OpenGL" in the compositor, the non-nVidia laptop has no issues. The laptop with the nVidia card flickers terribly when OpenGL is selected, but does not when Software rendering is chosen.
As a control, KDE using OpenGL compositing does not flicker.
I am on Arch Linux. I am Running a System76 Oryx Pro laptop with a discrete nVidia card and a 4K screen. Enlightenment is version 0.22.3. EFL is 1.20.7.