Something like micro-locusts could do that, or potentially a biological pathogen. For instance, suppose we released some bacteria to eat waste plastic and it just started eating everything organic.
I toyed around with genetic algorithms way back in the day when computers still only had one CPU core usually, so the networks you could realistically evolve with these algorithms were really primitive. The interesting thing about that back in the day was that already after a few iterations, these networks tended to get so complex in their interconnections that, when you took them apart, it actually got really hard to figure out why they actually worked the way they did. I mean, you could see the results, but even with these networks that really only had a handful of "neurons", it was already difficult to figure out how the simulated evolution interconnected them when you selected for fitness in specific manners. So yes, unintended side effects in technology like this aren't only possible, they're *incredibly* likely. I can promise you that the creators of ChatGPT still have no idea about most of it's little quirks and kinks. That's what I meant with my self driving car example, the training is so incredibly subtle and when you spend some time on what little worthwhile you can find in the general public regarding scientific papers and technical documentation, it's basically mostly "Well we tried this and it worked but actually we aren't sure why". Granted, that's a lot of scientific papers for you but the way how little things can amplify the results in different directions is *enormous* with this tech. So much is really just guesswork at this stage, and tons of ground is uncovered. What you also see a lot in this space is "we toyed a bit with the parameters and surprisingly, it made the results magnitudes better" so that's also crazy. I honestly also don't believe self-driving cars are as straight forward reachable as with the current approach but I'd never fully discount (or -count for that matter) anything at this point. Simply too early for that.
I like to draw parallels to the home computer revolution because I lived that too and there are lots of similarities. When you had a computer in the 80s, did you really need that computer? Nah, you didn't. Was it useful to have it? It could be, but often it was actually not really and there was little you could do with it you also couldn't do in more conventional (for the time) ways, sometimes a lot easier/better even. Lots of people also thought computers for everyday use will basically never be a thing, many even considering them a fad. But you know, it paved the way and in the very end, it always had it's uses to be exploited, and it only got better and better when the technology and methods evolved. This stuff feels very similar.