I’m running Audacity 3.2.4.0, macOS Catalina Version 10.15.7 on a MacBookPro (13-inch, Mid 2012)
I downloaded the Mac version of FFMpeg from https://lame.buanzo.org/ffmpeg.php and followed the instructions found at https://support.audacityteam.org/basics/installing-ffmpeg, installing it on Macintosh HD.
It still won’t open FFMpeg-required files, saying it doesn’t have FFMpeg
I went to Preferences: Libraries and found “libavformat.dylib” in /Library/Application Support/Audacity/libs but it wouldn’t accept it, it just closes the window.