If anyone with a strong stem background wants a minimal path to understanding this (or at least seeing what it takes to understand this) on a deeper level I have to recommend Leonard Susskind’s “Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe”. It pulls no punches.

Read it with Feynman’s mantra in mind: (paraphrasing/retooling The mantra for lesser mortals like myself) just dive in, read until you don’t understand, then go find a book for that part, and read until you don’t understand, etc etc. I recommend having a “strong stem background” first or else this tactic may never terminate. Maybe Lenny’s Susskind’s theoretical minimum course could fit the bill for most of the background too, but I can’t vouch for how much GR is covered.