As you know, Google and Facebook were not public in 1999 and Facebook was not even a thing.
I was there when Google started - I know some #-single-digit employees personally. I was stupid value investor enough not to join/invest.
Apple was not the-real-Apple (TM) in 1999 yet.
We already talked about Amazon-vs-Ebay on the other thread.
Even assuming we avoided pets.com, investing in 1999 would have been Amazon, Yahoo, Ebay, ??? and out of these only Amazon worked out eventually. There is a big risk that that's the same situation right now. Although one could argue that AI requires huge companies with huge data sets and Google/Facebook/Amazon/Apple/Microsoft will win vs any startups.
Looking from the positive point of view, for any non-value-investors, there was a very long time - 20 years so far !!!! - to invest into Google/Apple/Amazon/Facebook sometimes at quite attractive valuations. The only requirement was not to sell when valuations went above "value investor sell threshold". I mostly failed on that too. But this might be a good way to invest in AI going from today. The positive is that you can follow the companies and sell off the ones that don't deliver. It's not easy, but it is somewhat possible. E.g. even though I stupidly value-investor sold most shares that I acquired through the last 20 years, I have to say - pretty honestly - that I did not buy (m)any shitcos that did not deliver. So it is possible IMO to pick mostly winners.
Anyway, what I own from AI now: Google, Microsoft, Nvidia, Amazon, Facebook. I own tiny position in TSLA. I own Apple, but I doubt it's going to be great AI play. I own tiny positions in some shitcos. I don't think there are other obvious AI investments right now. I'm interested to hear if someone has suggestions though.