On Using UV Channels With Static Meshes in Unreal Engine | Unreal Engine Documentation
The documentation is copy-pasta from 4.27. There is no Polygon Editing Plugin in 5.0, replaced by the modeling tool afaik, as well as the menu and screenshots do not apply anymore as well.
Creating UV Mappings needs a modeling update though the whole page, while well-written, needs new UI/UX info
