The basis of Core Web Vitals is data from actual user visits. These are always influenced by the users' environmental conditions and their interactions. Lighthouse, on the other hand, is a tool that collects lab data. That is, it simulates the process under constant conditions. Thus, at a given point in time, Lighthouse can provide information on what the data looks like for some users and what opportunities for improvement exist. However, this may differ from the data collected based on actual user visits. Hence the difference with the Chrome UX Report.