It's a simple question. I'm just trying to understand how these things fit together. Core Text doesn't seem to get updated much, but maybe that's because it's low level and doesn't need it. I assume it's still the recommended way to do low-level text things not handled by TextKit. ?
Is TextKit 2 built on Core Text?
Yes, TextKit 2 is built using Core Text, as is Text Kit 1. This is mentioned in the WWDC 21 video "Meet TextKit 2".