Reddit is definitely not a forum the same way old-school forums were forums. And I don’t believe you can, with a straight face, say that they’re the same.
Also, “Forums are platforms where the main purpose is to discuss the topic of any given thread”. That’s a very broad definition. Depending on how loose you want to enforce that you can convince me that Twitter and YouTube are forums.
Plus, “discuss the topic of any given thread” you say this in a thread about TikTok collecting more data while you’re clearly talking about something unrelated to that.
These definitions are blurry. If I told you “we should set up a forum” you’d not instinctively think we’re creating Reddit, and for good reasons.
But I’ll agree that HN is probably the more forum than social media if we were to place it on a scale. And that’s how these platforms should be judged imo: on a scale.