I tested this with 3 Nvidia Drivers to see if I could find a driver that works properly. I tested the following Game Ready drivers Version 457.30, 461.40 and the latest, 461.72. The flicker occurred on all three of them.
Tested in //UE4/Release-4.25 @ CL 14469661 and this did occur, so not marking as a Regression.
The File, Edit, Window, and Help dropdown menus flicker and are displaced
There would be no flickering after enabling window animations
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-110464 in the post.