O voo está confirmado.

Because estar is normally used for a state or condition, while ser is used more for identity, classification, or more permanent characteristics.

In O voo está confirmado, the idea is:

• the flight has the status of being confirmed
• this is the current situation

Using ser here would sound unnatural in normal Brazilian Portuguese.

A useful comparison:

• O voo está confirmado. = The flight is confirmed.
• O voo é internacional. = The flight is international.

So está confirmado describes a current condition, not an essential characteristic of the flight.

It functions like a past participle and, in this sentence, it is commonly understood as part of a resulting-state expression with estar.

So está confirmado means something like:

• is confirmed
• has been confirmed and is now in that state

Portuguese often uses estar + past participle to describe the result of an action.

Compare:

• A porta está aberta. = The door is open.
• O voo está confirmado. = The flight is confirmed.

So while confirmado comes from the verb confirmar, here it behaves very much like an adjective describing the flight’s current status.

Portuguese uses definite articles much more often than English.

So o voo literally means the flight, and in many everyday contexts Portuguese prefers the article where English might be more flexible.

For example:

• O voo está confirmado.
• A reserva está pronta.
• O embarque começou.

You can sometimes omit the article in certain contexts, especially in headlines, labels, or very reduced messages, but in a normal full sentence o voo is the most natural form.

Because voo is a masculine noun in Portuguese.

So:

• o voo
• um voo

And because voo is masculine singular, the participle/adjective also appears in the masculine singular form:

• confirmado

If the noun were feminine, the form would change:

• A reserva está confirmada.

In Brazilian Portuguese, voo is pronounced roughly like VOH-oh, with the two o vowels forming a hiatus rather than a single long vowel.

A simple approximation in English would be:

• VOH-oo or VOH-oh

The stress is on the first syllable:

• VO-o

So it is not compressed into one syllable in careful pronunciation.

Yes. Under older spelling rules, it used to be written vôo with a circumflex.

After the spelling reform, the standard modern spelling became:

• voo

So in current Brazilian Portuguese, voo is the correct spelling.

You may still see vôo in older texts, but it is now outdated.

Yes, and the meaning is close, but the focus is different.

• O voo está confirmado.
  Focuses on the current status: the flight is confirmed.

• O voo foi confirmado.
  Focuses more on the event of confirmation: the flight was confirmed / has been confirmed.

In many practical situations, both are possible. But if an airline agent is telling you the current status, está confirmado is especially natural.

Yes, absolutely.

• O voo está confirmado. = The flight is confirmed.
• Seu voo está confirmado. = Your flight is confirmed.

Seu makes it directly personal and is very common in customer service.

You might also hear:

• O seu voo está confirmado.

In Brazilian Portuguese, both seu voo and o seu voo are possible. The version with the article can sound a little more natural in many contexts, depending on region and style.

Yes. In this kind of structure, confirmado agrees in gender and number with the noun it describes.

Examples:

• O voo está confirmado.
• A reserva está confirmada.
• Os voos estão confirmados.
• As reservas estão confirmadas.

So the ending changes depending on what is being described.

It is completely normal everyday Brazilian Portuguese.

It sounds natural in situations like:

• airport announcements
• airline apps
• check-in counters
• customer service messages

It is neither unusually formal nor unusually casual. It is just standard, natural Portuguese for giving a status update.