@Victor12 i found a code in .htaccess that seems to solve the cache issue.
I do not know if this code is good or not for the forum simply disable cache and for me seems work on new content.
Issue on old content will persist you have to clear all browser data.
How i tested? Created a new post, edited, go back on main Flarum than i reopen the discussion and i see edited text no more the old wrong text.
You can try to add this but without any guaranty from my part and any reasonability.
Header unset ETag
Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate"
Header set Pragma "no-cache"
Header set Expires "Wed, 11 Jan 1984 05:00:00 GMT"
Added this on top of the .htaccess on public folder.