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.