For months this issue has been reported by lot of users and there are multiple open discussions in the community. Following is the link to one of those https://nothing.community/d/4317
And not only in YouTube, also in Hotstar I’ve observed the low brightness issue.
Nothing has a good track of listening to the community and fixing the issues brought out through updates. But the team haven’t even acknowledged nor responded in any discussions on HDR playback issues.
Seems like Nothing is deliberately going blind on this particular issue?