La falta de conformidad aparece en el formulario de devolución.

In this kind of Spain Spanish, falta de conformidad is a fairly formal or legal expression. It refers to a product not matching what it should be, for example because it is defective, incorrect, incomplete, or does not meet the agreed conditions.

So although the literal parts are lack of conformity, in real use it often means something like:

• non-conformity
• lack of compliance
• a defect / problem making the product non-compliant

In consumer-rights contexts in Spain, this is a very common phrase.

Because falta is a feminine noun in Spanish, so it takes the feminine article la.

• la falta
• una falta

This has nothing to do with natural gender; it is simply the grammatical gender of the noun.

The subject of the sentence is the whole noun phrase la falta de conformidad, and that whole phrase is singular.

So the verb must also be singular:

• La falta de conformidad aparece
• not aparecen

Even though the subject has several words, its head noun is falta, which is singular.

Aparece is the:

• third person singular
• present tense
• of the verb aparecer

So it means appears, shows up, or in this context often is shown / is listed / appears on.

Examples:

• El nombre aparece en la lista. = The name appears on the list.
• La información aparece en la pantalla. = The information appears on the screen.

Aparece suggests that the item shows up, is found, or is written/displayed in that document.

That is slightly different from:

• está = is located / is there
• es = is

So aparece en el formulario sounds like:

• it appears on the form
• it is shown on the form
• it is listed on the form

This is very natural Spanish for information contained in a document.

Because Spanish commonly uses en for both in and on in many contexts, especially with documents, pages, screens, lists, and forms.

So Spanish says:

• en el formulario
• en la lista
• en la página
• en la pantalla

Even if English would often prefer on.

De devolución describes what kind of form it is: a return form.

Spanish very often links nouns with de where English uses a noun directly as an adjective.

So:

• formulario de devolución = return form
• literally, form of return

Other similar examples:

• tarjeta de crédito = credit card
• centro de salud = health centre
• política de empresa = company policy

Because de is extremely common in Spanish for linking nouns.

Here it does two different but related jobs:

1. falta de conformidad
   = lack of conformity / non-conformity
   Here de links the idea of lack to what is lacking.

2. formulario de devolución
   = return form
   Here de tells you the type or purpose of the form.

English often uses noun + noun combinations, but Spanish usually prefers noun + de + noun.

Spanish uses definite articles more often than English does.

Here:

• la falta de conformidad refers to a specific issue already identified in the context
• el formulario de devolución refers to a specific return form

Even when English might sometimes omit an article in a heading or label style, normal Spanish usually keeps it.

Yes. Spanish word order is more flexible than English, especially when the meaning is still clear.

For example, you could also say:

• En el formulario de devolución aparece la falta de conformidad.

This version puts more emphasis on where it appears.

The original sentence is completely natural, but moving en el formulario de devolución to the front is also common.

Not exactly.

• defecto usually means defect
• falta de conformidad is broader and more formal

A falta de conformidad may include a defect, but it can also mean the product does not match the contract, description, model, expected quality, or intended use.

So in legal or consumer language, falta de conformidad is often more precise than simply defecto.

Sometimes, but not always in the same context.

• no conformidad is common in technical, industrial, or quality-control language
• falta de conformidad is especially common in consumer-law language in Spain

So for a return form or legal consumer context, falta de conformidad sounds very appropriate.

Not always. In document or interface language, aparece often means:

• is shown
• is displayed
• is listed
• appears

So in this sentence, depending on context, a natural English idea might be:

• it appears on the return form
• it is listed on the return form
• it is shown on the return form

Spanish uses aparecer very naturally in these situations.