"HDR" is just metadata to pass along to the device to tell it how to optimally adjust the colours (or not adjust them). It's main use seems to be so that HDR displays can oversaturate "SDR" content in HDR mode.
> carries more data
Not really. The metadata isn't more colours or something, it just passes info to the device about certain aspects of the video.
HDR content will be HDR if the display has enough range regardless of whether or not the OS has HDR "mode". It's more about adjusting all the other content.
Dunno if you ever had a plasma TV back in the day but they could display way more contrast than LCDs of the day so you could adjust the settings to change the way all content looks. HDR metadata is basically that, but on a per-video basis. Useful enough but not some game changer... Which is why there's tons of articles about what HDR does and doesn't do.
Edit - where HDR really is great is photography... You take multiple photos of the same scene with different ISO and shutter settings then stitch them together for more colours than would otherwise be captured. But a screen can either display colours or it can't.