De-ess the vocal track on it’s own before applying any effects, (like reverb*).
Once in the mix it’s usually not possible to de-ess without collateral-damage to the percussion …
[ * reverb & basic-compression will both exaggerate sibilance ]
ToneBoooster’s has two free real-time de-esser plugins which work in Audacity on Windows,
1 complicated, called “sibalance” [sic], & 1 simple.
There is also Audcaity-specific “desibilator” plugin, (but it does not work in real-time).