I do not know a plugin that could check the spelling of all already stored pages.
However, all articles in the wiki are just .txt files in the folder [wiki directory]/data/pages
. So if you have a tool that could do this analysis on them you have made a first step. So maybe it is a way of thinking to do the analysis outside the wiki, and publish the output somewhere in the wiki?
A first hit from google: https://plaintextproject.online/articles/2020/08/04/spell.html