In Arcmap AND Arc Catalog, when viewing the properties of a hosted feature service, it is possible to copy the field name, as the "copy" command is enabled with mouse focus over the field name:
In Pro, the copy field name functionality has been disabled. This is required when the field name, not the field alias, is required for use in some other application, e.g. writing a user guide, writing a py script, etc...where copying and pasting the true field name correctly is needed.
Copying the field name from the Pop-up does not work, as the Pop up only contains the field Alias.