Convert AUP3 to MP3

Converting Audacity 3 Project files directly to MP3 audio format (.aup3 to .mp3 conversion) is certainly doable, but you won't be able to find any third-party programs, or conversion utilities, to accomplish that.

Your only option is to use the latest Audacity version (3.X and newer), since it introduced the AUP3 format for its projects. All you need to do is load your project in Audacity, and simply bounce it as an MP3 file.