The "Additional Details" section shown in the Shopify Admin's order detail page is stored in a field called note_attributes (also known as "cart attributes") in Shopify's backend.

Our app EZ Exporter can export this data by selecting the note_attributes.name and note_attributes.value fields in the Data Settings:

This will place all the field names in one column and all the values in another.

A more common use-case is to extract each attribute and put it in its own column in the exported CSV or Excel file. This can be achieved by using the Calculated Fields feature and entering a formula like this:

search_attributes({{ note_attributes }}, "Name of the Attribute")

Screenshot of what this looks like in the app:

The output will look something like this: