Unfortunately I can't point you at a single comprehensive resource.

Instruction for building apps in AppKit has always been kind of spotty. When I first started learning it alongside Objective-C in the 2000s, the best a beginner could really do was sift through random blogposts and mimic patterns seen in FOSS Mac apps. The best resources at that point were probably the various books on the topic (such as the Big Nerd Ranch Cocoa books I'd seen recommended frequently) but at that point I was a broke teenager so buying books was off the table.

I would like to at some point build a one stop shop for learning all the most pertinent parts of building a Mac app with AppKit and Swift, but that takes a lot of time… if it happens it'd probably be when I'm inbetween jobs so I can dedicate the resources required to make such a thing good.

Gotcha, thanks for the reply. I think you'd have the market on this domain cornered if ever you'd produced a comprehensive text since its very much still blog posts and reading extant code.