Is it possible or legal for social media to read/analyze people's conversations for their feed algorithm?

I use facebook which is a popular social media platform in my country. I noticed that my feed sometimes is related to the topics that I'm talking with my friends through chat. for example yesterday i was talking to my friend that eating pineapple hurts my mouth then minutes later, a short video about that pineapple phenomenon randomly shows up in my feed. This happened a lot of times now but i just thought it's more obvious and aggressive recently. …

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