HDR Darker on CoreELEC Odroid N2 than Internal Player

Single Board Computers Odroid N2/N2Plus/C4/C5
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I have the same/a similar issue. expecially dark scenes look pretty bad (no contrast, like a cheap 720p stream), while bright scenes are at least decent.

Similar to Problems described here and here

I have a Grundig GOB 9990 OLED (lg 2017 panel)