How does the Explore page algorithm primarily determine which content to show to a user who has never interacted with a specific topic before?

When a user has never interacted with a specific topic before, the Explore page algorithm primarily relies on the user's established interests and behaviors on the platform to determine what content to show. This involves analyzing the accounts they follow, the posts they've liked, saved, or shared, and the topics they've searched for. The algorithm then identifies content that is similar to what they've already engaged with and that is also popular among users with similar profiles. For example, if a user frequently interacts with posts about fitness and healthy eating, the Explore page algorithm might show them content related to yoga or weightlifting, even if they've never explicitly searched for those topics. The algorithm uses collaborative filtering and content-based filtering techniques to make these recommendations, predicting what the user might find interesting based on their past behavior and the behavior of similar users. Initial content is chosen based on broad interest categories derived from their existing activity, and then refined based on real-time engagement data.