Indeed. The word 'platform' doesn't appear in the entire section. The only time the word 'publisher' appears is:
(1) Treatment of publisher or speaker
No provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider.
And that's the trillion dollar line. The reason for its justification is because as an owner of a digital platform, you can't get sued by Joe for defamation because somebody said something defaming about him on your platform.
Publishers can, and do, get sued for defamation because they're responsible for what they publish. Now let's imagine a hypothetical extreme where OnlineSite ends up censoring any posts related to Joe, except those that defame him. It's quite clear that the site themselves are now actively defaming Joe, but they can use 230 to hide behind that line making them legally immune.
In short, the more censorship a site engages in, the more they are effectively publishing their own views and those they defacto endorse.
The question is when is “information provided by another information content provider?”
Suppose Facebook (corporate) generates content, sells it to an independent company, then leases it back and publishes it?
Suppose Facebook uses millions of user-submitted pictures to train an AI, then publishes the resulting images? Are those “information provided by another information content provider?”
Suppose Facebook copies and pastes user content, but claims to be the author and puts “written by Facebook and representative of the company’s official views.”
Suppose they have samples that say A and B, and they choose to show A and not B?
Suppose they like the gist of A, but it would be more compelling if they edited the image, changed the wording, and cut out other parts?
Suppose they like A, but hires staffers to completely rewrite the story, like Disney redoing Cinderella?
The legalese defines this: "The term “information content provider” means any person or entity that is responsible, in whole or in part, for the creation or development of information provided through the Internet or any other interactive computer service." In all your examples except the 4th Facebook would clearly be the publisher/provider, and responsible. The 4th is where things get tricky largely because of yet another part of the law:
"No provider or user of an interactive computer service shall be held liable on account of any action voluntarily taken in good faith to restrict access to or availability of material that the provider or user considers to be obscene, lewd, lascivious, filthy, excessively violent, harassing, or otherwise objectionable, whether or not such material is constitutionally protected"
Wrangling over the term "good faith" is going to be a lot trickier, especially when plausible deniability enters into the picture.
Contrary to popular belief, it doesn‘t make a clear distinction between platform and publisher.