I'm putting this on here mostly for Samsung support to see the issue and hopefully fix, but if others have a solution or are experiencing the same, please post here.
I have the 75" QN90A. Great display but there is a backlight flickering issues when when displaying HRD Content. At first I thought it was just a one off situation, but it is definitely specific to HDR are prevalent on a variety of content and sources.
Netflix Last Chance U - Bball has this very evident in most scenes where the team is in their gym practicing. The light/grey colored backgrounds and walls in the scene cause an issue and the QN90A backlight light starts flickering. Some settings on the TV can reduce this, but it's still an issue and shouldn't require adjusting settings to levels that are not optimal for viewing.
Here is a setting where you can clearly make this happen:
Local Dimming High
Contrast Enhancer Off
You can change Local Dimming to 'Standard' and this mostly goes away, but that increases the overall brightness of the display further. By toggling Contrast Enhancer on and off, you can also sometimes reduce this, but not cure it. The underlying issues seems to be that the overall backlight level has to be really high to avoid this and by adjust some of the Contrast Settings, Gamma, and others, it raises it just high enough for it to overcome the flickering.
It's very distracting and unpleasant. It seems to be a software related issue (I am running the latest update) and hasn't been fixed.
This also happens in the Amazon App. Jack Ryan for example. I recorded a sample of the flickering so you can see what to look for.
The common theme is a white/bright grey background. It's worst with Local Dimming on High, but not limited to just that.