You don't find a box for a middle name in the UK either.

Anyway, this is absurdo.

I have British Nationality, I have Spanish Nationality.

I have two names and one hyphenated surname in the UK (or did have until I married).

I have two names and two surnames in Spain. That's two first names. Not a compound, two separate names.

Nobody, not friends, not family, not the Banks, not the Palacio de Justicia, not the University I went to, nobody in Spain has ever had the tiniest problem grasping the concept that I have two names and only use one of them.

Yes, some people do see their two names as a unit, others don't. Let's put José Antonio Dominguez Banderas out there as an example.

Since I'm intimately connected with a country that genuinely does not grasp the concept of a second/middle name, stating that Spain and Spaniards are also unable to grasp the concept is something I don't accept.