First, don't get me wrong, I trust you that you see white backgrounds flicker when brightness set to low on your ZF6. I just wonder if it is isolated HW problem on a few devices, or widespread problem, but only a few users are able to perceive it, hence I asked if it is easily perceivable by users or not.
That's exactly why I asked this. If it is in night mode less visible, many users may not perceive it when using night mode on a daily basis.
You are wrong, it is not silly at all.
I have seen many times that users were unable to confirm any standard behavior on their device, but when they concentrated, sharpened their senses and turned on their brains, they eventually succeeded
It's like having the ability to perceive the flicker of an old 50Hz CRT screen, or hear the whistle of line decay (15625 kHz on old PAL CRT TV).
If you want to perceive subtle random changes in the brightness of the screen in a dark room, you have to concentrate on it, watch it for some time to get your eyes accustomed to the darkness, and your brain to notice those changes. When someone goes out for a moment, turns off the brightness, glance at the screen for a moment, then is probably able to say that their display is ok.
That's why I asked detaily how easy it was to notice.
In other forums, someone even shot a video that was supposed to capture the flicker, I didn't see anything like that because it was filming from a shaking hand, and the distance and angle from the camera to the screen was randomly changed, which in itself affects the brightness of the picture.