There's an obnoxious story on Ars Technica (which I generally adore) with obnoxious comments about the immoral, technical and marketing failings about The Mandalorian on Disney+ and how it's not really HDR (high dynamic range) and the false advertising will lead to the end of days and people should be fired and all sorts of nonsense. These are undoubtedly the same people who felt that 720p on a 26" TV wasn't high definitiony enough, even though your eyes can't really tell unless you get close.
HDR is basically the ability to show a wide range of contrast, from really dark details to bright details. Digital cameras have gotten to a place where they're about as good as film, and about the range of your eyes when they're in good health. Displays are getting there, too, especially the beautiful OLED screens on most phones and better TV's that are dropping quickly in price.
But just because this technology exists doesn't mean that it has to be used. If you've been around computer-based video for any length of time, you know how easy it is to tweak video by either teasing out details or eliminating them, often to serve some arbitrary aesthetic that you're after. That's not right or wrong, it's just a choice you might want to make as a maker of things. I would even argue that the look of a good film is best not grounded in something that looks like real life because it interferes with the fantasy of it all. Something shot at 60 frames per second with high dynamic range might be great for a nature documentary, but I wouldn't apply it to a Star Wars story.
As a technologist that nerds hard and finds creative endeavors deeply satisfying, I'm often struck by how few people can nerd and think like an artist. That someone would actually take the time to measure the brightness of a TV show to "prove" that it isn't HDR shows that they don't understand the intent of the tool. And if you don't get that, please, look at all of the crappy filters people still put on Instagram photos, or worse, what an average wedding photographer does to every shot.
We bought a 4K HDR TV last year for the playroom, and some of the content that takes advantage of the format from Netflix and Disney+ is really quite stunning. And that TV isn't even an OLED display, which would result in more true shadows and even lighting. At the end of the day, we still have a 9-year-old conventional backlit LED TV in the living room that looks OK most of the time, save for some spots that got dinged through 4 moves. I look forward to replacing it, even though it's not a priority.
HDR is like another crayon in the box, and it doesn't have to be used to make the storytelling great. Maybe the nerds will eventually figure that out.