The splitter arrived and as I thought it can't fix HDR and DolbyVision colors for ambilight.
The built-in chip is the GSV2001 for HDMI 2.0 1to2 splitting with 1080p downscale, ARC and CEC support. Nothing special.

Perhaps they downscale 4k sources to get minimal color enhancing, but this can't fix HDR or DolbyVision colors for right lightning. This is simply technically the wrong way to do it 😏.
The splitter will fix the missing ARC support and DolbyVision passthrough. That's it.
DolbyVision does not work with the splitter I received. Apple TV does a test and rejects Dolby Vision with this free screen.
exactly same problem as this user.
The display says it cannot display DV once the splitter is connected. Take the splitter out - DV works on display, but with the pink colour.
@Exokaz
Sadly DV does not get passed through as soon as I have the splitter installed. Picture goes through but DV cannot get activated (Apple TV 4K).
I would prefer that it worked - especially after the long wait. But it does not.
I have read a few comments here with the same result. So I guess you are lucky with your combination.
The splitter does not fix DV passthrough. Once it is installed there is no DV on the tv anymore. Others have had the same experience. So no, it does not even fix that