What are the best books/papers/blog posts to learn about Morphic's architecture? I'm not a user of any Smalltalk implementation but I'd like to learn more as the Smalltalk approach to UI is very interesting.

Morphic started on Self actually, maybe start there?

I am unaware how it evolved since then, especially given the differences between Self and Smalltalk.

https://handbook.selflanguage.org/2017.1/morphic.html

https://sin-ack.github.io/posts/morphic-intro/