I don't have an exact answer.
I had downloaded some 4K stuff and when I played it back on the TV from USB the picture was very dark, almost unwatchable. I looked online and seen this was a big thing for a lot of people with HDR TVs, not just from Hisense and HDR isn't really about brightening all the colours like many of us thought. That's when I came on here and questioned it all because there are older TVs than this that received updates from Hisense and those allowed those panels to display HDR. I didn't understand why this one was left out because if you go into the HDMI settings, it says it can display 8 and 10 bit colour and 2.2.
I then emailed Hisense twice, the second time I got a reply and both times I asked if there was an update for this model of TV, I have the 55" version and I asked them can you tell me if there is an update for this TV or will there be one in the future that allows HDR because I know you did it with other TVs over the past few years and I would love this TV to do the same and be the same as the rest. I also mentioned what I said in my own thread about the PS4 not recognizing it as a HDR TV. When you send your message to them online one of the questions they ask you is for the software number of the TV. When I got my reply a few days later the person said to me that there is in fact and update for this TV and they gave me the link for it and instructions on how to update the TV and I did that.
Here's where things can be a little tricky. They told me about the update and gave it to me and gave me the instructions. There was no mention of HDR but in a separate paragraph they said have you got the correct HDMI lead for the PS4. I've been using the same lead for 3 years so obviously I don't think it is a new one but that was them acknowledging the HDR without actually saying HDR so when that paragraph came after the update and the instructions, I read that as being this update will allow HDR.
The film I got which was with HDR was The Magnificent Seven. It was very very dark, unwatchable, when I played it again it was better, you could watch it but the colours were not jumping off the screen like I thought it was supposed to. I then played an SDR version of Wonder Woman which was fantastic, it looks amazing. What I then did was i played 4 samples of three separate things all of which are in HDR. I got the Kingsman Golden Circle, Blue Planet 2, Dunkirk and Wonder Woman. My PC cannot play HDR, I don't think many PCs can but when I played all of these samples on my PC they were all very dark, Blue Planet 2 in particular. When I then played them on the TV all of them looked fine. The clip with Blue Planet 2 had a bird flying over this city, on my TV there was blue skies and sun shining and you could see all the colours on the bird. On my PC it was just like a dark shadow flying across the screen.Kingsman was bright and sharp, very colourful, surprised me because it was like the SDR version of Wonder Woman, it looked amazing, Dunkirk was better but not to the extent of the other two but the big thing was the skin tones and the colour of the water, massive difference and Wonder Woman was very different, the thing I noticed most was the colour of the grass and the sky being very different shades but nowhere near what it was on my PC which again was unwatchable.
I can only think that's how those are meant to look. The more I learn about HDR the more I have learned what it's about. It's supposed to be more realistic. The problem is you cannot turn it on or off unless you have a UHD player or your source is connected via HDMI. I've been told there's only a few players that actually allow you to turn HDR on or off, the only other way to do it is in the HDMI settings and turn Enhanced off. I'm playing these videos via USB so it's more tricky for me because there are several versions of everything, there's 8 bit SDR, 10 bit SDR and of course HDR. It definitely plays the HDR videos fine now but I don't know to what extent they are. I don't know is it true 10 bit colour or not. I can only explain what I see and the Blue Planet 2 and Kingsman Golden Circle samples where like night and day prior to the update and after it and then comparing on my PC to the TV. Whatever the update did do it took those files and turned them from very dark dim videos into full colour videos. I checked the software number afterwards and it has been updated even though my TV is on a wired connection, it kept saying there was no update available. They gave me the update and it has been updated. It also rearranged the apps in a different way and the EPG seemed to be quicker when browsing it.
I had never seen HDR before I got this TV. I personally thought it meant something other than what it was. The only HDR videos I really liked was Blue Planet 2 and Kingsman Golden Circle. For the others I would watch the SDR versions but that's just my preference. I don't know the best words to use to describe it but it was too "movie like" for me. I just think that is how those films are meant to look, I think Magnificent Seven and Dunkirk are supposed to be that way. I just loved the others because they were so colourful. It's just my preference.