Everything except for the last part of this is native functionality built into Mac. Automator is an app every Mac ships with and it natively has the ability to put things in your Quick Actions, make folder actions, etc.
The only real hacky part of this is that it is stuck within the "Quick Actions" menu instead of just being part of the dropdown and this app addresses that. But thats a fairly small part of this implementation.
In MacOS, it is really convoluted. Do I dynamically load some bundle? What bundle? Likely they'll put it somewhere else sometime soon.
Of course in principle, there is some API but the way that Apple treats them is very different.
For example, I want to get how many fingers are touching the trackpad right now and the current position of these touches. There are all sorts of things like PinchControllers that need to be initialized and they emit events etc., but nothing to give you the current state of affairs or exactly what you want.
If you look at the page, the difference between the official implementation and this app is that instead of it being under "Quick Actions" in your context menu, it is just right there.
It isnt like Apple doesn't give you a way to put something in your context menu with Automator, they just put it inside Quick Actions. You don't even need to use Automator, just right click in finder, go to quick actions and click customize.
Would it be great if I didnt need it to be stuck under Quick Actions, I mean sure. But except for one minor change (making something 1 less level deep in a menu) this entire workflow is possible without any third party app or "hacks".
Edit: If we want to talk about API's and other things sure. But given the context of this article, I was assuming that the OP was talking about the functionality presented in this article which most of the implementation is Apple provided tooling.
Is using undocumented APIs in Windows common? This sets off my Spidey-sense hard.
In macOS, you'd write a Finder Action Extension[0], which lets users add buttons to Finder's toolbar and context menus.
> In Windows, you'd either have something documenting that API (to add it in the context menu, not under Quick Actions)
As someone who uses both Macs and Windows PCs, I absolutely loathe that this is so common in Windows. Every utility I install wants to add their own items to context menus, and they can do so without my permission. On the Mac, users need to opt-in to allowing your extensions, and they can always go to System Settings and disable them later.
[0]https://developer.apple.com/documentation/appkit/app_extensi...