I’m assuming this was built with AppKit?

If so, yeah AppKit has some warts, and it isn’t all that well documented. That’s how it’s been since I got started with it back in the early-mid 2000s, where your best sources for learning were random blog posts or books (the latter of which I couldn’t afford as a teenager).

If you ever do iOS dev, UIKit is a lot nicer to use in almost every way. It’s been polished and modernized a great deal in comparison, and because iOS as a platform is so much more popular/important it’s throughly documented end to end.

Still, AppKit does have some advantages, like its batteries-included nature which allows one to build complex apps with few or no third party dependencies.