I've been working on a MarkdownView library for iOS based on tree sitter: https://github.com/HumanInterfaceDesign/MarkdownView

Like the OP mentioned, it's still surprisingly difficult to build what feels like a trivial interface using SwiftUI. Once you get into rich text, selection, streaming updates, syntax highlighting, diffing, or just smooth scrolling, you very quickly end up fighting the framework instead of building the app