lack of licensing ??

What is the reason for no longer supporting *.m4a on Mac with Audacity ?

On Mac OS X, Audacity is supposed to be able to import M4A files using the QuickTime library. Unfortunately that is broken in the current version of Audacity, however, if you install FFmpeg then Audacity is able to use that to import M4A files. See here for how to install FFmpeg:

ok… does the nightly build have it ? or i’ll just go back to an older version which does support it natively.

If you can wait a few weeks the next release version should be out.

Nightly versions are not recommended for production work and may contain bugs and/or incomplete features, but yes I think the issue is fixed in the current nightly version.