Harsh, piercing SS sound is called “Essing,” and there is an Audacity tool for it.
https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283/1
DeEsser, also DeClicker.
I use these settings because I’m not very good at deciphering the instructions.
The tool is volume sensitive. If you apply it to a slightly low volume reading, it may not do anything even though you have serious essing in the reading.
I use it after the Audiobook Mastering tools.
Mastering conditions the reading to pass Audiobook standards so the loudness and peak sound values are always the same and you don’t have to go around the barn with different settings looking for the best DeEsser volume range.
Koz