@ct70: If this is most noticeable in low light conditions, please try heading to Settings > General > Intelligent Mode Settings > Adaptive Picture, and toggle this option off to see if you notice a difference. This optimises the brightness of the picture based on the lighting conditions in the room, so this is worth exploring as an option. Furthermore, head to Settings > Picture > Expert Settings > Local Dimming, and set this to Low. Please can you also try heading to Settings > General > Power and Energy Saving > Brightness Optimisation > Off.
Let me know how you get on.