When exporting a joined layer to a shapefile in ArcGIS Pro, the field names in the attribute table of the shapefile appear differently than the joined layer.
In ArcGIS Pro, the Copy Features geoprocessing tool uses the Qualified Field Name environment setting by default when exporting a joined layer. Qualified field names have the name of the origin feature class or table appended to the field name. The default structure of the qualified field name is tableName.fieldName. For example, a table named Customer with a field named CustID would have a qualified field name appearing as Customer_CustID.
To omit the feature class or table name of the joined layer when exporting to a shapefile, the Qualified Field Name environment setting must be disabled. The following steps describe how to disable the Qualified Field Name environment setting in the Copy Features tool: