I agree with Matt Ronge’s article “Mac apps are harder than iOS apps”.
I was surprised when a recent project brought me back to the Mac and I discovered how finicky Cocoa really is. I was particularly shocked because I always remembered Cocoa as a particularly nice set of APIs.
In my experience, a big problem that Mr. Ronge does not mention is that there is very little information available online to help a macOS developer work through anything but the most basic situations. Sure, you can find some tutorials on raywenderlich.com or YouTube, but once you go beyond the basics, good information is hard to find.
If you search for “How do I do X? on iOS” you will likely find dozens or hundreds of hits, including numerous tutorials, open source libraries, and Stack Overflow questions. Conversely, you will be lucky to find one or two resources for the query “How do I do X? on macOS” (or OS X).
It is understandable, because iOS is such a huge platform, but it is also quite frustrating, at least to a solo developer like me. If Apple creates a new framework or shim layer to let us use iOS frameworks on macOS, I think it would make making Mac apps a lot easier for predominantly iOS-oriented developers like me..