Bug: can't change quality when export to .m4a file

When exporting to .m4a file, changing quality slider between 10 to 500 has no effect on output file; file has always 196kb/s and the same size.
I use latest stable Audacity version 2.1.3, and ffmpeg 2.2.2 ( F(55.33.100),C(55,52.102),U(52.66.100) ) all extracted from zip.

Except that: Why it is needed ffmpeg2 not ffmpeg3? Why it is needed special version of ffmpeg2 and why this version is so outdated (2.2.2 vs 2.8.13) ?
Newer versions of ffmpeg have fixed many bugs and security vulnerabilities.

Since you’re uisn .m4a I assume that you are probably using iTunes/iPod.

If that is the case, then eyou would be much better exporting WAVs from Audacity, importing those into iTunes and then using iTunes to do the AAC conversion.

That is what I did with my LP/tape collection digitization and it worked well.