They all claim to be platforms, because it would be near impossible to regulate every single thing that gets posted on their site. That doesn't mean they can't regulate or censor things that are posted, or because they do that they become publishers who are now responsible for things put on their site. This has been the way the internet and internet platforms have worked since section 230 went into effect.

Platforms have removed content they find objectionable since they have started. AOL in 1997 would ban users who cursed in chat rooms. That didn't make them suddenly publishers who had to make editorial decisions and responsible for the things millions of users on their service posted.