I've posted this under other topics, but it might be missed by developers who don't use ArchiCAD for architectural work. Under macOS 10.5, ArchiCAD will not recognise a bundle as an add-on if it lacks a 'PkgInfo' resource. Make sure you check the option 'Force Package Info Generation' in XCode (sets GENERATE_PKGINFO_FILE=YES).
Note that this option isn't set in the example files in the DevKit.
Ralph Wessel BArch
Software Engineer Speckle Systems