This is the way I see it right now:
The format of the frames sent through HDMI to a TV set is different if it’s SDR, HDR10… HLG…DV… Each one has its own metadata/headers… format…
A SDR video frame differs from an HDR video frame (that’s why tone mapping processing is needed to convert an HDR-only track to be coherently displayed in a SDR display). But both (SDR and HDR) are one-track only.
And DV frames from discs are real-time built, by DV compatible UHD players, using the HDR track and the annexed DV track to send a “new DV enhanced frame”. That’s why some times is named “dual layer”.
Latest x265 and some mkv tools are experimenting with it. Partial success with mp4 files. Nowadays, mkv seems a trickier due to lack of native “dual stream” support. And DV only tracks (like the ones streamed by Netflix to displays/devices which support it), would be only compatible with DV displays, so potentially useless/incompatibe for HDR10 only devices.
Due to this, don’t expect anytime soon a massive presence of DV files available out there. More or less like DTS tracks in the very first months (years?) during DVD first years (20 years ago).
Who knows… ?