For me, the last straw was when someone (who I thought was my friend) reacted harshly to a technical statement I made. And that was on the Fediverse, which has no algorithm manipulating people's feeds.
However, it was last year when I realized that social media is entirely a time-sink -- absorbing my time and giving me nothing in return. I think 2018 was the last time I actually got something objectively useful from social media.
i wonder what changed
I think a few things have changed. One of them is that people are feeling the squeeze as the economy crashes and inflation increases. People are reflecting the stress from that at people on social media.