I haven't looked at this in a bit, but I thought that companies are exempt from their users' speech only if they don't make editorial decisions (and Twitter does, like reddit or HN or Slashdot). Am I mistaken?
On the contrary, Section 230 is what allows platforms to make some editorial decisions without thereby assuming liability for all user-generated content.
Before 230, what you said was true.
I like this explanation: https://www.techdirt.com/2020/06/23/hello-youve-been-referre...
https://www.theverge.com/2019/6/21/18700605/section-230-inte...