I would like to be able to export as MP3 a “slowed down” song, or part of. I want the exported mp3 to be played on an external mp3 player at the slowed-down speed. Is this possible?
Apply either “Change Speed” effect (changes pitch and tempo) or “Change Tempo” effect (changes tempo, retaining the same pitch), then Export.
https://manual.audacityteam.org/man/change_speed.html
https://manual.audacityteam.org/man/change_tempo.html
https://manual.audacityteam.org/man/file_menu_export.html