Hello…new to the forum and I did try to find this by searching, but no luck…everything seemed to be for importing.
I’m trying to export an aud file to mp4. I downloaded and installed the ffmpeg file, but I still do not see an mp4 option. Is it even supported? If so, how do I use it.
Hello…new to the forum
Welcome 
You will need to use Export Audio
https://manual.audacityteam.org/man/file_export_dialog.html
And select “Custom FFmpeg Export Options”
https://manual.audacityteam.org/man/custom_ffmpeg_export_options.html
You will find mp4 in the left column - when you click on that the Codec column will show the available Codecs
WC