Helper libraries increase the functionality of Audacity. FFmpeg helps with the import and export of a broader range of file types than the basic Audacity install. Currently, licensing issues prevent them from including it. The library only has to be installed once.
This will be needed to import m4a audio files which are created by Zoom.
Here are the instructions from the Audacity Support website
https://support.audacityteam.org/basics/installing-ffmpeg