Core Web Vitals are a set of real-world, user-centered metrics that can help to quantify key factors of a user's experience. They focus on 3 areas: speed, responsiveness, and visual stability. Google combines these factors in determining search ranking as they help provide a holistic picture of page experience.
The Core Web Vitals data is collected and updated every 28 days. This means that the scores reported on the Snapshot report are what Google measured in the previous 28 days. So if recent changes have been made to improve these scores, they will not be reflected immediately.