https://thenextweb.com/neural/2021/01/26/heres-how-ai-determines-what-you-see-on-facebook-news/
it uses multiple layers of machine learning models to predict what a user wants to see.
The ranking system first collects candidate posts for each user, including those shared by their friends, Groups, or Pages since their last login.
Next, a lightweight model narrows the pool of candidates down to a shortlist. This allows more powerful neural networks to give each remaining post a score that determines the order in which they’re placed.