[MX Player] scarp:
Well, I'm not sure whether it's the files to blame. As I mentioned above, my Note10+ N9760 Snapdragon does have something wrong while playing some HDR videos some of which are released by Tigole, TERMiNAL, PSA, etc, as listed below. It's also the same case with my Note8 N950N Exynos.

Big Hero 6 (2014) (2160p BluRay x265 10bit HDR Tigole).mkv

Big.Hero.6.2014.2160p.UHD.BluRay.x265-TERMiNAL.mkv

Zootopia (2016) (2160p BluRay x265 10bit HDR Tigole).mkv

Jojo.Rabbit.2019.2160p.10bit.HDR.BluRay.6CH.x265.HEVC-PSA.mkv

Knives Out (2019) (2160p BluRay x265 10bit HDR Tigole).mkv

Ford.v.Ferrari.2019.2160p.UHD.BluRay.x265.HDR.DD 5.1-KangMus.mkv

Dark Phoenix (2019) (2160p BluRay x265 HEVC 10bit HDR AAC 7.1 Tigole) .mkv

The easiest spotted problem is the red color cos it looks like the red is reduced by almost 30% to 40%, though some other colors also look washed out more or less but not so distinguishable to me as the red color. And their maximum brightness is no higher than their SDR versions, while some of them are even lower.

Actually, the sad thing I have just found out is that even the HDR10 movies that I always thought played perfectly with MX Player Pro on my Note10+ because the brightness is higher than usual such as <The Secret Life of Pets> #1 and #2 are actually not played in the right color!!! I just compared them with their regular non-HDR version. The red color is sadly surprisingly still somewhat paler with the HDR playback!!! Red looks about 10% reduced. Not so bad as other HDR movies so you don't instantly tell or even see it as correctly played because the excellent brightness cheated you into believing so until you compare the it with its SDR version. So really this leads me to feel no HDR movie is completely supported on cellphone yet.

The Secret Life of Pets (2016) (2160p BluRay x265 10bit HDR Tigole).mkv

The Secret Life of Pets 2 (2019) (2160p BluRay x265 10bit HDR Tigole).mkv

For example, The Secret Life of Pets (2016), check 00:06:25~00:06:45 the red stand mixer machine used as a massage machine by the sausage dog. Not really red. (Looks to you quite real red? Try compare it and you 'll see it's actually orange-ish red)

It's the same case when the same HDR movie's playback is compared between my Note10+ and my computer.

(PS: Those 2 movies are by far the only 2 HDR movies that I find produce the highest brightness, quite noticeable but sadly still only 10% higher than their SDR versions when both version are at maximum brightness)

The best scenario is a bitter sweet thing which is that I do find below HDR movies produce correct color, but the brightness is way lower than their SDR version by about 15% to even 40%. So SDR versions turned out to be even much more enjoyable on the phone.

Frozen (2013) (2160p BluRay x265 10bit HDR Tigole).mkv

Frozen II (2019) (2160p BluRay x265 10bit HDR Tigole).mkv

Cars (2006) (2160p BluRay x265 10bit HDR Tigole).mkv

Fast.and.Furious.Presents.Hobbs.and.Shaw.2019.2160p.HDR10Plus.BluRay.8CH.PSA.mkv

Yet, on the other hand, I do find all the 10 demo HDR videos I have are perfectly played back on my Note10+ with MX Player Pro. Red is genuine red, not even a little less as played on my computer. Besides, the brightness is way higher than the HDR movies brings though the HDR movies are for sure correctly recognized as HDR and do have brightness boosted when you check the Android UI interface during the playback. But they just do not work the same way. Like the demo videos doubled the brightness while HDR movies just don't get brightness gain. Like HDR movies are played in an isolated section that brightness boost does not apply.

Samsung.HDR.4K.DEMO_Chasing.the.Light.Main10@L5.2@High.ts

LG.4K.DEMO_NASA-HDR.mp4

Sony 4K HDR Demo - Mont Blanc.mp4

Samsung 4K HDR Demo - Wonderland 1.ts

Sony Swordsmith HDR UHD 4K Demo.mp4 (Got this one here from this thread)

ETC.

So, I don't know what's the cause and reasoning. Seems a little complicated.

But at least when it comes to HDR movie files, I do tend to believe that it does not make any difference which team group released the mkv file. The source file, such as the remux file, is probably what makes the difference.

HDR on cellphone is more like a bragging fact. HDR movies are still not fully well supported.

NOT ENJOYABLE for movies.