[HELP] Can you share the setting?

[Selur]

Wild guess: You didn't enable HDR Signaling&Co
Assuming you are using x265 and are reencoding HDR-10 content:

• x265->Signaling->General Signaling->HDR
  
• x265->Signaling->HDR-10/HDR-10+->LightLevel
  
• x265->Signaling->HDR-10/HDR-10+->Master Display
  

should be enabled (optionally x265->Signaling->HDR-10/HDR-10+->Chroma smaple location)
als I would enableall the options under "x265->Signaling->Video Usabilit Information->Color" where the value from the input isn't unknown.

Cu Selur