O protocolo e a denúncia estão no aplicativo.

Because the subject is plural: o protocolo e a denúncia = the protocol/report number and the complaint/report.

In Portuguese, when two singular nouns are joined by e (and), they usually make a plural subject, so the verb must also be plural:

• O protocolo está no aplicativo. = The protocol number is in the app.
• A denúncia está no aplicativo. = The complaint/report is in the app.
• O protocolo e a denúncia estão no aplicativo. = The protocol number and the complaint/report are in the app.

Because Portuguese nouns have grammatical gender, and each noun normally takes its own article.

• o protocolo → masculine singular
• a denúncia → feminine singular

So you cannot use just one article for both nouns here. Portuguese usually repeats the article when the nouns have different genders.

No is a contraction of:

• em = in/on/at
• o = the

So:

• em + o = no

That means:

• no aplicativo = in the app

Other common contractions work the same way:

• na = em + a
• nos = em + os
• nas = em + as

Not usually in the English sense of protocol.

In Brazilian Portuguese, protocolo often means a reference number, case number, filing number, or confirmation number connected to a report, complaint, or official process.

So in this sentence, o protocolo probably means something like the number or record associated with the complaint.

Denúncia usually means a complaint, report, or formal accusation/reporting of wrongdoing.

In Brazilian Portuguese, it is often used when someone reports a problem, crime, abuse, fraud, or another issue to an authority, service, or platform.

Depending on context, it could be translated as:

• complaint
• report
• formal report
• accusation

Portuguese uses estar for location in most cases.

So if something is located somewhere, you normally use estar:

• O documento está na pasta. = The document is in the folder.
• Eles estão em casa. = They are at home.
• O protocolo e a denúncia estão no aplicativo. = The protocol number and the complaint/report are in the app.

Using ser here would sound wrong, because ser is not normally used to say where something is located.

You might see article omission in certain styles, like headings, instructions, or very compressed written language, but in a normal full sentence, the articles are usually expected:

• O protocolo e a denúncia estão no aplicativo.

Without the articles, it sounds less natural in ordinary speech and writing.

The accents help show pronunciation and stress.

• denúncia: the acute accent in ú shows the stressed syllable is nú
• estão: the tilde in ão shows a nasal sound, and this ending is very common in Portuguese

So roughly:

• denúncia → de-NUN-cia
• estão → es-TÃO

The accent marks are part of the correct spelling and should not be omitted in standard writing.

In Brazil, aplicativo commonly means app, especially a mobile app.

So:

• o aplicativo = the app

A native English speaker might expect something more like application, but in everyday Brazilian Portuguese, aplicativo is the normal word for an app on a phone or similar device.

Yes, to some extent.

You could say:

• A denúncia e o protocolo estão no aplicativo.

This is still grammatical. It just changes the order of the two nouns.

You could also sometimes move the location phrase for emphasis:

• No aplicativo estão o protocolo e a denúncia.

That is more marked or formal, but still possible.

The most neutral version is the original:

• O protocolo e a denúncia estão no aplicativo.

In careful pronunciation, it would be roughly:

• O protocolo e a denúncia estão no aplicativo.
• oh pro-toh-KOH-loo ee ah deh-NOON-see-ah es-TOW no ah-plee-kah-CHEE-voo

A few notes:

• e often sounds like ee
• ão in estão is nasal
• in many Brazilian accents, ti in aplicativo sounds like chee, so aplicativo sounds close to ah-plee-kah-CHEE-voo

This is only an approximation, but it helps with the main sounds.

It is neutral and natural. It works well in everyday written Portuguese, customer service messages, app instructions, and general communication.

It is not especially formal, but it is not slangy either. It sounds like standard modern Brazilian Portuguese.