I would like to set specific accounting codes by country, but the tab is empty.

Context

WooCommerce Accounting only offers adjustment of accounting codes for the country of sale of your shop.

If you can’t find the countries you are looking for, your store might not be set to sell in those countries.

Solution

Set up countries in the "General" tab of WooCommerce settings.

You must have activated the delivery for the list of countries to be displayed, even if your site does not use delivery.
Specify in the WooCommerce settings: “Deliver to all countries where you sell.”