SO's downfall started way before AI. A decade or so ago it was always full of interesting questions, people were giving detailed answers, there was sometimes some debate in the answers, etc

And then it started being stupid questions. People who clearly had barely tried anything and just rushed to SO with a half baked question. Answers were just pointing to another thread that already provided the answer. It definitely started before LLMs. I think it lined up with the aggressive "learn-to-code" push.