Interview in chinese. The 2nd section discusses the 100-400 f4.5/5.6S
This also mentions the flickering lights issue, though not for the EVF but for the electronic shutter.
"Question: In the case of electronic shutter, it is easy to cause stroboscopic problems due to indoor lighting when shooting indoors. How did Nikon solve this problem? Answer: Set the flicker reduction in the photo shooting menu to "ON" to reduce the stroboscopic problem caused by the flickering of the lighting under fluorescent lamps or mercury lamps and other light sources. When the light frequency is 50 Hz, the flicker period of 100 Hz is detected, and when the light frequency is 60 Hz, the flicker period of 120 Hz is detected. However, if the flicker period of the light source is variable during continuous shooting, the effect of flicker cannot be reduced. "
It seems the flicker reduction is designed to handle the normal electrical grid frequencies but LED lights can flicker at other frequencies. "Striped flickers may still occur under some LED lighting. For this we plan to launch a solution in 2022." Hmm. interesting, so they are working on the problem. I hope they address EVF flicker also and not only banding in the images taken with electronic shutter, and also I would like to see firmware updates to include less expensive models as well, not just the Z9.
With regards to the 100-400, it's interesting that they discuss all the troubles of the previous lenses though not specifically referring to them as flaws of the 80-400. ;-) They talk about quality control and design to minimize problems due to manufacturing tolerances at the extended zoom setting as well as lens balance and the resistance of the zoom when shooting from angles. It really sounds like they are getting the right feedback and are trying to correct problems of earlier lenses.