https://www .acx.com/help/acx-audio-submission-requirements/201456300#192kbps-MP3
Personally I would de-ess before making an mp3,
as any excessive sibilance will have a lot of digital artefacts after being encoded to mp3
You’ll need a high-resolution de-esser, which has multiple bands, like Paul-L’s free one,
(all the other free de-esser plugins I’ve seen just have one band, and are not going to tame your sibilance).
Store-bought de-esser plugins can process the audio quicker than Paul-L’s, and are easer to use, but they co$t.