HN is not one of the sites listed. Although, you could select 'other', but I did not consider HN social media. Maybe my definition of 'social media' is a lot narrower than the US government's. I mean, does being a member of a classic bulletin board count?

Which social media are listed outside of FB, Twitter, and IG? Can't seem to find this. The article mentions it includes email. Is this included?

I renewed my ESTA back in February, then they had a section with social media accounts but it explicitly said that filling that section out was voluntary.

when I did esta 2 weeks ago social media hadnt been mentioned

No its there. Filled it in 3-4 weeks ago and there was already a field for it back then. Was marked as optional though