alt Hacker NewsDunno. The internet was definitely smaller, but it was also largely uncorrupted, so you could literally just email a random university professor or an industry expert and get answers to dumb questions.
And today, if you want to learn something the right way, you probably still should buy a book (or, I guess, pirate an ebook). I don't think you can really learn much from YouTube influencers and the like.
I respectfully respect the premise that the choices are "paper books" or "Youtube influencers", though I'll note we didn't have Gilbert Strang's 18.06 course back in 1999 either.
I'd also note that the Internet of 1999 was loaded with spam, bursting at the seams with it, so much so that it was actually a big deal when ~30 months later Paul Graham wrote a post about Bayesian filtering.