I believe it was the Netflix documentary The Social Dilemma (2020) that demonstrated exactly this in an experiment with a woman who willingly participated. Researchers showed how browsing data and search history can be used to tell when someone might be more vulnerable or persuadable (she had had a miscarriage during the experiment, which of course was very exposed due to search history), which can then be used to serve ads promoting beauty or health/dieting/fitness products.