I don’t understand what it means to be “solved”. It’s like saying that “architecture is now solved”, “physics is solved”, or “programming is solved”.

It’s a field of science and/or engineering, it’s not like we will ever run out of things to try/build/investigate. LLMs work… to a certain extent, with limitations and tradeoffs, and for some things. Would you spend days, money and Co2 to split a huge text corpus in sentences with a LLM, if a simpler program can do that just as well, there’s no need to find “the perfect prompt” (and hope that the LLM doesn’t forget one sentence, adds something inbetween, etc etc) and it gets done in three hours?