I haven't been able to get HDR working on my desktop amdgpu + X11. I don't think it's supported in Wayland yet either (let me know if I'm wrong) and the devs in #mpv on freenode said they don't have HDR10 output support either (although mpv can do HDR10 tone-mapping).

For HDR videos, I still play them via my Windows box. I think the current MacOS supports HDR too (and if not, it will get support soon as they have that crazy new $6k HDR screen).