The presentation has “ice pick in the ears” sibilance and “essing.” I can well imagine what listening to that on headphones would be like.
You also have compression (talking into a milk jug or wine glass) distortion.
This is quite a low quality 56kbps export.
Oddly, that’s not it. You can produce a perfectly acceptable non-stereo presentation at 56 and nobody will notice. The mono limit is somewhere in the 30s. However, you can’t produce your voice track in MP3. Every time you edit or do corrections or production in MP3, the sound quality goes down and you can’t stop it. If you do enough careful editing and cleaning, the voice will start to sound like bad cellphone.
Record your voice and export a safety copy as WAV (Microsoft) 16-bit. Mono WAV quality is somewhere up in the 700s, and it doesn’t change. Do all the editing in Audacity Projects or WAV and then, way at the end when you’re getting ready to ship the final product, then make the MP3. So that should solve the honky sound. That, not coincidentally, is the recommendation for audiobooks.
Sorry, once it does that, the track is trash There is no good way to take that kind of damage out.
Are you using a home USB microphone such as the Blue Yeti? Those are famous for overly crisp, sharp, gritty, piercing sound. I think the makers assume that sounds “professional.” It makes my ears bleed.
There is a DeEsser which can help.
I have some notes on how to use it here, somewhere.
As we go.
Koz