I think you're defining "forum" too narrowly ("websites that look like the forums of the 90s and 00s, like Bitcointalk 
"). Twitter, Instagram, even TikTok are also "forums", only with a slightly different interface. These are platforms allowing people to discuss, react to other posts, and categorize posts thematically (if that's done via folksonomies - e.g. hashtags - or ontologies - subforums defined in some kind of a "top-down" manner - isn't that important.) There are even some successful forums which are very close to the 90s instances, particularly Reddit and their clones.
"). Twitter, Instagram, even TikTok are also "forums", only with a slightly different interface. These are platforms allowing people to discuss, react to other posts, and categorize posts thematically (if that's done via folksonomies - e.g. hashtags - or ontologies - subforums defined in some kind of a "top-down" manner - isn't that important.) There are even some successful forums which are very close to the 90s instances, particularly Reddit and their clones.On the contrary, dear d5000, your definition of a forum is too broad. Are you comparing TikTok where people show their faces and do little dances with this anonymous forum? Or Instagram which is a social network where people show idyllic lives? On Instagram or TikTok there are hardly any discussions.
You have failed to include in the definition of forum the social network BeReal, where people not only show their faces but when they receive a warning they record what they are doing at that moment (except if they are shitting, I guess). I can't imagine Satoshi, if he created bitcoin now, creating an account on BeReal (or Instagram or TikTok) to talk about it.
The main difference between forums and social networks is anonymity, and that the forum is written-only.