The problem here is that OBS doesn’t tonemap the HDR image back to SDR for broadcast on traditional streaming platforms.
According to YouTube’s article, the only software they claim supports streaming HDR content directly to YouTube is Mirillis Action.
Stream HDR video on YouTube - YouTube Help (google.com)
It’s been my experience that Action’s HDR support is terrible though :-\ I have my doubts about this, but it’s apparently supported.