I use ArcMap 10.7 to publish 24 Feature Classes as Layers in a Map Service. I then add the individual layers from the map service REST URL to ArcGIS Online for use in our organization. The 'Item Details' in ArcGIS Online is blank for Summary, Description, Tags, Credits, etc.
As an example desired end-state, the USFWS has a National Wetlands Inventory Service https://www.fws.gov/wetlands/arcgis/rest/services/Wetlands/MapServer When this service is added as an item to ArcGIS Online, the Summary, Description, Tags, and Credits are automatically generated. This is what I'm trying to do.
I have tried right-clicking on a layer > properties > General tab and the information entered does not appear in ArcGIS Online. I have also tried the description tab for the feature class in ArcCatalog to no avail.
This support page from esri confused me very much but may hold the answer? https://doc.arcgis.com/en/arcgis-online/manage-data/metadata.htm#ESRI_SECTION1_CE02409EE61D4A51A2BB943A2D8D982F