Dell consultant has confirmed

Color depth is true 8bit. Backlight is one edge LED strip.

It was also clarified that the Flicker Free and Low Blue Light has a hardware solution.

That's why the monitor has 3 stars by TÜV Rheinland Eye Comfort Standard V.3.0

ID No. 0217010014: DELL Inc. - Certipedia

I wonder what was missing for 4 stars?