Hi,

If you want to update the existing record, there is an option while exporting "I want to update data" (import-compatable export) option ticked, the system only shows the fields that can be imported. This is helpful in the case where the existing records need to be updated. This works like a filter. Leaving the box unticked, gives many more field options because it shows all the fields, not just the ones that can be imported.

For more information please check the below documentation.https://www.odoo.com/documentation/18.0/applications/essentials/export_import_data.html

Hope it helps