The audio on that track only goes up to 8KHz, (a buzzy guitar would have lots of harmonics and should go up to almost double that ).
Unless you deliberately filtered out the frequencies above 8KHz, then a sample rate of 16KHz has been applied somewhere, ( sample rate should be 44.1KHz or 48KHz for a music recording). This limitation could be due to you having a too low a bit-rate selected when converting to mp3 which is sacrificing the higher frequencies (in this case those above 8KHz).
I wouldn’t use a bit-rate below 128Kbps for a 48KHz mono (not stereo) mp3, for music.
see here for how to change the mp3 bit-rate in Audacity … MP3 Export garbled - #3 by Trebor
A harmonic generator can add back some of the higher frequencies which have been lost, but you’d get a much better result by re-recording the performance and saving in WAV format.