Plex does not show the "legacy" Metadata Agent by default now. This should be in the doc
https://support.plex.tv/articles/200241558-agents/
Legacy Metadata Agent Settings
As of Server version 1.43.0 Legacy agents wil not longer be shown when creating new libraries or editing libraries using modern agents based on the setting Server Settings>Library>Show Legacy Agent during library set up. If there are already libraries with those legacy agents enabled those libraries will have the options displayed.
Plex does not show the "legacy" Metadata Agent by default now. This should be in the doc
https://support.plex.tv/articles/200241558-agents/