You can access the full list of available metrics and their details directly in the latest Dynatrace. Press CTRL/CMD+K, type dt.frontend and select Show more.
The New RUM Experience, which brings RUM to Grail, introduces numerous built-in metrics with the prefix dt.frontend. Because it uses a different data model than RUM Classic, there are no direct equivalents for RUM Classic metrics, which use the prefix builtin:apps. However, many metrics have replacements that serve an analogous purpose, as shown in the table below. Note that metrics with the prefix builtin:apps that do not appear in the table have no replacement.
Differences in metric values between the builtin:apps metrics and their replacements are expected and result from underlying data model changes.