Yes, TextKit 2 is built using Core Text, as is Text Kit 1. This is mentioned in the WWDC 21 video "Meet TextKit 2".

Here you go: https://developer.apple.com/documentation/uikit/textkit/enriching_your_text_in_text_views There's not much meat in there, unfortunately, and the lists are very buggy (on macOS, try clicking at the end of a line). It also seems there's a lot of stuff not yet available in the first Ventura/Xcode 14 beta. For instance, the NS/UITextView constructor init(usingTextLayoutManager:) seems to be missing.