The short explanation
Where HDR10 sends one set of brightness figures for a whole title, HDR10+ sends them per scene, or even per frame. The display gets specific guidance for the dark corridor and separate guidance for the snow field, so tone mapping no longer has to compromise across both.
Technically it does much the same job as Dolby Vision. The difference is commercial: HDR10+ is royalty-free, Dolby Vision is licensed.
Where you run into it
Support is split along brand lines. Some manufacturers back HDR10+, others back Dolby Vision, a few do both. Content is split the same way, so which format you actually get depends on the title as much as the hardware.
All of it still rides on the capability data. A display that supports HDR10+ will only receive it if the source was told the capability exists.
How the DR HDMI 8K handles it
The DR HDMI 8K lists HDR10+ support explicitly and offers it as an EDID flag setting, on its own or combined with HLG. Three of its custom default EDID tables are built around HDR10+ displays, so you can present a known HDR10+ capability set rather than assembling one by hand.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.