Can't import m4a files to Audacity
Audacity (as of v2.4.1) is not looking for libavutil.*.dylib, it needs ffmpeg.*.dylib. That is not installed by homebrew.
You will need to download ffmpeg.*.dylib by following the instructions at https://manual.audacityteam.org/man/installing_ffmpeg_for_mac.html
It should automatically install the ffmpeg library and configure the Audacity Preferences &gt; Library to:
/Library/Application Support/audacity/libs/ffmpeg.55.64bit.dylib
Then you will be able to import m4a audio files.