So wanted to add this to help others
I've had the "too Dark" issue since getting the TV.
I have found the Engineering Menu fix works..... for most sources
But I still have problems with the Netflix App itself, the input app is sooooo dark its almost unwatchable in dark scenes.
I have tested this against the Netflix app on my YouView Box and found that the YouView one is perfectly fine..
So not a fault of the TV, just the TV software and the 3rd party Apps...