In terms of SEO, forums, I believe, still have a slight edge.
But given how forum content has continued to slide in ranking over the past few years, I really can't be sure how long it will keep its edge.
You have to understand that “social media posts” is a blanket term.
There are platforms that you can call “social media” that can rank your content better.
In fact, a lot of SEOs use these platforms as “parasites”—I’m talking about Reddit and Quora.
Until recently, Medium.com was a great choice until they made some key changes.
Sadly, given forums' SEO trends recently, I don’t really have much reason to be optimistic of it getting back its old SEO “clout,” so to speak.
If I were you, I’d stick to finding the right social media platforms.
Use SEO tools like Semrush to really get to the bottom of how you can use such platforms as parasites for your content.
A lot of these social media platforms have a tremendous amount of domain authority.