I read through the Mac Portal Wiki and I see some examples of using Cocoa specific APIs (like Drawers and Sheets), but I could not find a specific guide/example on how to access AppKit API, but probably it's there and I can't find it.
I don't think there is any guide specifically applicable to your request, but you can check out the
/usr/local/share/fpcsrc/3.x.x/packages/cocoaint/src/appkit source directory for what's available.
Could you point me please to a simple example/source code where I can see how to add a simple NS<component> to a form?
Pure FPC examples can be found in the Wiki article
FPC PasCocoa. You should probably look at all the
Cocoa Internals articles.
Offhand, I don't know of any examples mixing the LCL and the native controls other than my recent Drawers contribution to the Wiki.
Could I mix AppKit widgets with NS AppKit widgets freely in the same form?
I'm not sure I even understand the question! Don't take that the wrong way, I'm only a simple lawyer who's just spent 4 hours converting an outdated Apple C code daemon example into non-deprecated C code daemon example so that I can now convert it into a Pascal daemon example.
I've probably helped as much as I can now, maybe someone else will take up the challenge.