While Mini-LED is great for watching HDR video and deeper blacks, but if you are going to read a book late at night, then be prepared to witness some halo-like effect.
Mini-LED is a Stunner on the 12.9-inch iPad Pro but can Get in the Way While Reading Books or Websites at Night
Mini-LED on the 12.9-inch iPad Pro might not be perfect in one key area - reading. See, while an OLED display can turn off individual pixels completely to create a pitch-black effect in the tiniest of places with sheer finesse, such as the space inside the letter 'O', this is something which Mini-LED just cannot do at a pixel level.
If you are planning to do some reading on the 12.9-inch iPad Pro, then you might run into a halo-like effect around text in dark mode. The effect could become more prominent if you crank up the brightness late at night.
According to Dieter Bohn in his M1 iPad Pro review for The Verge:
There was one odd bug I experienced. Putting either the Kindle app or Apple Books into dark mode and viewing them in a near-pitch black room, I noticed a strange gray haze around all of the text blocks. It’s too big to be blooming; it’s more like the local dimming algorithms got a little confused. It’s a minor thing that I hope gets fixed
I am not entirely convinced how this issue will be fixed in a software update. Sure, the LEDs underneath can be programmed to light up exactly where they should when reading text on a black background, but whether or not it will compete with an OLED display, like that on the iPhone, remains to be seen.
But, the hopeful fanboy inside me says that this issue will be fixed to the point that an average user will not notice the halo effect at all.