Nothing wrong with MX Player in my S10+. It plays 10-bit HDR10 4K HEVC just fine (HW+ enabled). Video output look the same in the stock player and MX Player.
Well, my Note10+ N9760 does have something wrong while playing some HDR videos. Biggest wrong thing is that the red color is washed out a lot that once you see you can easily and definitely tell something with the color is not right.