Brazilian here. Around these parts, middle names are not a thing. They don’t show up in forms, and also aren’t expected to exist.

When the names before the family names are multiple, we call them “nomes compostos” (composed/combined names). There are very common combinations, such as “Carlos Eduardo” and “Maria Clara”.

If someone named “Maria Clara Guimarães Schindhelm” fills out a form, they’ll say their given name is “Maria Clara”, with the rest being the surname.

Knowing where the given name ends is an exercise in pattern recognition. We have a sense of what’s a given name, and a sense of what’s a surname. It’s an imperfect system, though: some families have surnames that are also used as first/given names (a common one is “Francisco”).