I've got an nu8000 and hdr content whilst watching Netflix etc is fine but with the ps4 pro when enabling an hdr it becomes incredibly dark, this can be seen on horizon zero dawn, the screen becomes really really dark, going back into the ps4 menu whilst the game is active shows the normally vibrant blue to be very dark. To get similar brightness as non hdr I have to turn on contrast enhancer to low and notch up gamma by one. Where you would expect bright whites, they are comparably very dim.
Everything matches up with hdmi black level and rgb inside the ps4 settings. It's only on hdr content.