Almost every forum post in the last like 10 years or whatever have relied on old markdown. All of those posts are essentially broken now (including the FAQs thread not showing table of contents [alongside me having to probably update the contents to the new site layout]) because it seems that markdown is either disabled or changed. Can someone explain the new markdown so I can fix my more important threads?

it seems that markdown is either disabled or changed

The redesigned site uses a completely new text formatting system. Basically, the site uses normal markdown now.

I think people do want a table of contents added back, since currently there isn't one, but I can't really remember if site staff have said anything about it.