Why: This Version of Audacity Was Not Compiled with QuickTime Files Support
If you are trying to import an MP4 file into Audacity and you already have the FFmpeg library installed, you may receive a message that prevents you from loading the file.
In most cases, the actual MP4 file you are trying to import likely does not contain any audio in it! Open the MP4 file and ensure it plays an audio track.
All else, the MP4 is likely corrupted. You can try to convert the MP4 online using sites like OnlineVideoConverter or OnlineAudioConverter.