Welcome !
The language for Cocoa (Swift and to a decreasing amount Objective-C) arent huge & complex
Cocoa, and all the other toolkits like AppKit etc are definitely gigantic topics in their own right
I’ve liked the Aaron Hillegass books
And they have decent blog posts etc (although they really want you to hire them or go to the Big Nerd Ranch)
I just had a quick perusal and they dont seem to have as many mac specificbooks or training courses as they once did
Thats too bad as the cocoa books are/were excellent