The new full page check monitor with extra metrics is now in public beta stage. Check out the Full Page Check page for a description of new features and how to switch this on for your monitors. This beta feature is available for Business and Enterprise accounts.
The API has been updated to also include the extra metrics. The Core Web Vitals and the W3C navigation timing metrics can be retrieved using the /MonitorCheck/{monitorCheckId}/Waterfall endpoint. Note that this works only for full page check monitors with the browser type set to Chrome with extra metrics and only in API version 4 (current version).
Remember that all changes related to the extra metrics for the full page check are part of the public beta program.