Things may have changed since then, but when I first encountered the project several years ago it seemed like the thing that made this project stand out compared to other player projects was a big emphasis on correctness and accurate playback. There have files I’ve encountered that for example VLC will play with quirks (color reproduction is not quite right, etc) that mpv plays perfectly.
Playing HDR and Dolby Vision encoded movies has been solved a long time ago in mpv, but they usually need the option shown above, which may not be the default on your system.
There are plenty of additional options in mpv that provide a finer control of how HDR colors are handled.
While playing a movie with mpv, press "I", so that mpv will display the information it has about the color space supported by your display and the color space used in the movie, which will allow you to verify if they are correct.
"mpv" or any other player must make a conversion from the color space used for encoding the video file to the color space supported by the monitor. A monitor that has not been reconfigured after the initial installation is likely to use the sRGB color space. Any good monitor should have a configuration menu that allows the selection of a better color space, but mpv can convert BT.2020 to sRGB, if necessary (which will reduce the saturation of many colors).
Did mpv print after being launched a line starting with "VO: [gpu-next]"?
Where "gpu-next" is not available, mpv will start anyway, but it will use one of the other video drivers, none of which convert correctly Dolby-encoded video.
On the computer where I normally play HDR/Dolby Vision movies, I use an NVIDIA GPU, so I know for sure that gpu-next works fine with it.
I do not remember whether I have played any HDR/Dolby Vision movie with an AMD or Intel GPU, but I doubt that any of those is incompatible with gpu-next.
In any case, if mpv prints "VO: [gpu-next]" without any error message and if "I" shows for "Display:" the correct color space supported by your monitor, e.g. sRGB or DCI-P3, then you should try to upgrade the GPU driver, which could be too old. Like I have said, IIRC this problem has been solved in 2022 and since then I have never encountered again color conversion errors, so you must have some software component that is older than 2022.
Because my monitor is configured to use the color space DCI-P3 (with 10-bit colors), I alias "mpv" to "mpv='mpv --vo=gpu-next --target-prim=dci-p3'", and it has been working fine for the last two years, including with any HDR and/or Dolby Vision movie.