iPhone XR iPhone XR and no HDR?

HDR has nothing to do with the resolution. HDR is all about how much the display can show in stops from dark to light (basically).

 

My assumption is you could play 1080p and the iPhone would downscale it to fit the screen

 

HDR has nothing to do with resolution.

Please educate yourself on what HDR is. It is clear you don’t understand (nothing wrong with that!), so it would be good to read up on it if you’re interested.

 

HDR is more about the dynamic range.

At the risk of greatly simplifying, HDR is letting the supported contents (which are most commonly HDR10 or Dolby Vision formats) utilize all or most of the display's "luminance" range (or brightness level). The end result is that you will see contents that can utilize both extremely dark and very bright details.

Hard to explain with words, but imagine contents where some portions are set to the lowest brightness setting and some portions set to the highest brightness setting. Add more color and advanced color management to the mix, you get the gist.

If you have iPhone with OLED screen (X, XS, XS Max), this YouTube channel has a ton of demos.

iPhone XR supports and plays HDR contents, but without the high dynamic range. So it's effectively not HDR.

 

YouTube has the option of -HD- Not HDR.

2 different things.