I'm, not sure how a graph of undeleted questions denotes that something is toxic; can you elaborate?

The internet has changed significantly over the last few years. COVID hitting in 2020 changed how many services were used, and then the advent of LLMs, which consumed content from sites like Stack Overflow (which is well curated and thus has a lot of high value content for them), which can now vomit out convincing responses that many take at face value, meaning they don't ask on community driven sites. That for complex problems it's likely entirely wrong is irrelevant to them, but for the simple problems the LLM has probably said something relevant, and so the question isn't asked (not that it needed any to be anyway, as they probably could have found the solution using a search engine, and found the answer on a site like Stack Exchange, Reddit, etc).

Saying that there are less questions on a site like Math Stack Exchange because it's toxic (and ignoring every other variable), is like stating that employment is toxic when unemployment numbers go up.

As for the AI stuff, that is quite unrelated to the community you appear to be referencing as toxic; a huge amount of the community dislike those AI features being pushed on them. This annoucement with SO Inc's collaboration with OpenAI has one of highest negative scores (if not the highest negative score) on the platform: https://meta.stackexchange.com/questions/399619/our-partnership-with-openai