I actually turned off HDR as soon as I got an HDR-capable TV, because it's apparently code for "eye-searingly-bright whites, including in the Apple TV interface itself." I don't understand who wants this. Maybe I'm a vampire?
I remember when HD TV's came out and it was mind blowing the difference between an old and a new TV. We had 3D TV, 4k TV's come out during that time period and they were fine, but viewing content in HDR was the first time in a decade I realised "wow there has been another shift". My partner would struggle to call the difference between our 4k TV and our older 1080 TV, but she absolutely adores the HDR on the newer LG.
100% luma is going to be "the brightest object shown in all of your media collection" which is probably the sun. Since on my computer monitor, 100% luma is usually used by UIs to represent a blank piece of paper, I toggle the brightness on my monitor when watching a movie.
It’s like having the bass turned up but for video.