Hi Robert Logan ,
That would be a ice feature to have. However, as you have noticed currently this feature does not exist. There is a related idea for ArcGIS Online here: Share Arcade expressions within AGO org but as you mention it would also be very helpful to have this functionality in Enterprise.
For now you could store the arcade expressions somewhere are copy and paste them in order to use them in other web maps (I store mine in .js files, but with a growing number of files, this is not a very good way). You can also save layers that contain Arcade expressions and then share them across the organization. However, if you save a layer that has an Arcade expression using FeatureSetByName and the other layer is not present or does not have the exact name in the web map, the expression will not work (although it will be present and you can correct the expression).
