Make sure you have selected the platforms you wish to build. On a Mac, you only have access to the build environment for Apple platforms (macOS, iOS and tvOS). Because the the Wwise Authoring application runs through Wine on Mac, it expects a Microsoft Windows DLL as authoring plug-in libraries built using a vc14x toolset, and so is unavailable on macOS.
The easiest way to then test your Authoring plug-in DLL on macOS would be to generate the bundle and install it from a directory or an archive in the Wwise Launcher.