Lol. I always feel the "toxicity" claimed of SO is way overblown. It's always "closed as dupe but not really a dupe and I got downvoted for asking a legitimate question". But 99% of the times it was really a dupe, or a poorly worded question, or something strictly off topic. Getting told that isn't toxicity. It's what keeps the community somewhat sane. If you try to look through the review queues, you'll see all the low effort posting the community has to deal with.
What I feel is killing SO isn't the community, but the leadership. They've ostracized their own moderators and reviewers for a long time. And with no stewards, it will become toxic. And a wasteland of low effort duplicate questions.