I'm an 80s born millennial who was lucky enough to be online before Eternal September, so I know the same time periods you're talking about and yes, social media, advertising, phonefaggotry and a number of other issues definitely made things less desirable thanks to a shift in who was using the Internet/web and why. However, all you can do is try to find some things of interest to you and if you're up to it, pass on the spirit of what made the old net great; not old technologies, but the approach and the vision that differed from what would come later. That's a big topic but anyway..

>Fediverse
Overall this is the best option we have for "harm reduction" for those that want the features of modern social media but without the bullshit; federated FOSS projects mostly but not exclusively based on ActivityPub. There are lots of different approaches- https://fediverse.party/ is a good place to learn about the various projects and also has links not just to the projects but places that analyze servers and the like. Mastodon/Pleroma/Misskey are Twitter style microblogging, Friendica / Diaspora are macrosocial Facebook style, Pixelfed is Instagram-like, Lemmy/Kbin are Reddit style, PeerTube is a promising YT alternative, and there's even Fchannel (the usagi fork) that is a federated imageboard still updated. Don't worry too much about CP - its not going to be on clearnet very often and even niche sites are moderated and take down shit when possible. Pic related is outdated but mostly still accurate.

The biggest potential weakness is shitty fucking admins for instances that break the point of federation importing blocklists of instances that are 'problematic/degenerate/tranny/fascist' on tenuous "receipts" of proof thereby affecting their users. However, you can find your own server or servers of interest that don't really do this sort of thing (some of the tools linked from the fediverseparty menu can help with finding them). Out of room