Don’t you need a OLED screen in order to get HDR?
HDR is mainly about 3 things
High contrast ratio:
Contrast ratio is the difference between brightest and darkest level.
OLEDs naturally have insanely high contrast ratio as individual pixels can be turned on and off and various levels in between (XS has 1,000,000:1 contrast ratio).
LCDs need local dimming that divides the display into several regions and apply different brightness level for each region. Without local dimming, LCD applies the same brightness across the entire screen, making darkest part washed out (grayish) or the brightest part less bright (full brightness across the entire region would consume more energy and light source, neither of which are yet possible for consumer grade displays). Older iPad Pros and iPhone XR (1,400:1 contrast ratio) do not have local dimming. Maybe new iPad Pro has local dimming but I doubt it.
Wide color gamut:
Ideally with 10-bit (HDR10) or 12-bit (Dolby Vision) display panel. All Apple devices, except 27" iMac and iMac Pro have 8-bit display panels (27" iMacs and iMac Pros have 10-bit). iOS's automatic color management feature maps P3 color gamut to 8-bit display, well enough for very good HDR-level experience.
High luminance:
Ideally 4,000 nits (HDR10) or 10,000 nits (Dolby Vision)
peak brightness, but no consumer display approaches anywhere near that.
SDR is typically 500 nits
peak brightness and HDR10 and Dolby Vision recommends (but not require) 1,000 nits
peak brightness. Great HDR TVs can approach 1,000 peak brightness over small region.
New iPad Pro has 600 nits, iPhone XR and XS have 625 nits. iOS uses tone mapping to adjust HDR10 and Dolby Vision brightness for the device's limitations.
Since older iPad Pros can playback HDR contents, I am guessing new iPad Pros can also. High contrast ratio is probably out as Apple hasn't offered local dimming on any LCD so far. But I am guessing new iPad Pro will at least benefit from wider color gamut.