> Apologies in advance to who(m)ever posted this article FYI, and this is just a tangentially related grammar remark, but "whomever" wouldn't be correct here,

> Apologies in advance to who(m)ever posted this article FYI, and this is just a tangentially related grammar remark, but "whomever" wouldn't be correct here, because the phrase "whoever posted this article" has the person in subject position here, even though the whole phrase is used in an object position (i.e "apologies to [whoever posted this article]"). You can think of it like "whoever" replaces something like "the person who," and "the person whom posted this article" sounds more obviously incorrect. You could use "whomever" if it were something like "whomever your friend met," as the subject is "your friend" in that case, and "whomever" refers to an object. The equivalent noun phrase would be "the person whom your friend met." Of course, most people just don't say "whom" ever, so it barely matters anyway.