That’s sibilance and you can suppress it with a DeEsser plugin.
The only downside I’ve ever found is the DeEsser tool is absolute. It’s up to you to get the work within range of the tool, or know where the work is so the tool can be adjusted to find it.
There is no “Go find the Essing and call me when you’re done.”
I found it handy to take voice work through Audiobook Mastering first to get the voice at a standard volume, and then apply DeEssing. That’s not a bad idea anyway because the Audiobook people use a fairly standard sound format.
This is the crazy long version. It’s actually only three tools. Scroll down to Process.
https://wiki.audacityteam.org/wiki/Audiobook_Mastering
Follow that with the DeEsser tool from here.
https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283/1
At these settings.
Enjoy. Post back if you get stuck. This process produces even volume, matched sound files with little or no Essing.
Koz