A maioria chegou hoje.

Because maioria is a feminine noun in Portuguese, so it takes the feminine article a.

This has nothing to do with the gender of the people being talked about. Even if the group is all men, you still say a maioria because the noun itself is feminine.

Examples:

• A maioria chegou.
• A maioria dos alunos chegou.

Because the grammatical subject is a maioria, which is a singular collective noun.

In Portuguese, as in English with the majority, the verb often agrees with the singular collective noun, not with the individuals inside the group.

So:

• A maioria chegou hoje. = standard and very natural

Even though the idea is plural, the grammar is singular.

In standard grammar, A maioria chegou hoje is the safer and preferred form.

You may hear plural agreement in speech, especially when there is an explicit plural noun after it, such as:

• A maioria das pessoas chegaram hoje.

But in careful writing, many teachers and grammar guides prefer:

• A maioria das pessoas chegou hoje.

With just a maioria by itself, chegou is the best choice.

Because Portuguese often uses the simple past where English may use either arrived or has arrived, depending on context.

So chegou hoje can naturally correspond to:

• arrived today
• has arrived today

Brazilian Portuguese does not use its present perfect in the same way English does.

Usually, yes. In normal speech and writing, a maioria is the natural form.

So:

• A maioria chegou hoje. = normal
• Maioria chegou hoje. = unusual in ordinary language, possibly telegraphic or headline-like

For a learner, it is best to treat a maioria as the standard expression.

Yes. That is a very common fuller version.

A maioria often refers to most of a certain group, and the group can be added with de + article + noun:

• A maioria das pessoas chegou hoje.
• A maioria dos alunos chegou hoje.
• A maioria dos convidados chegou hoje.

Without that extra phrase, a maioria means the majority / most of them, with the group understood from context.

Yes, the word order can change.

A maioria chegou hoje is a very neutral, natural order:

• subject + verb + time expression

You can also say:

• Hoje, a maioria chegou.

That puts more focus on today.

Portuguese word order is somewhat flexible, but the original sentence is the most straightforward version.

Not in this sentence, because no destination is mentioned.

Here, chegou simply means arrived. If you want to say where they arrived, Portuguese usually adds a preposition:

• A maioria chegou ao trabalho hoje.
• A maioria chegou em casa hoje.

So the basic sentence is complete without a destination.

In Brazilian Portuguese, maioria is pronounced roughly like:

my-oh-REE-ah

The stress is on ri:

• mai-o-RI-a

And the whole sentence is approximately:

• A maioria chegou hoje
• ah my-oh-REE-ah sheh-GOH OH-zhee

That is only an English approximation, but it helps with the stress pattern.

Not always.

A maioria is closer to the majority or most of the group. It usually refers to a specific set of people or things, even if that set is only understood from context.

So it works well when there is an identifiable group:

• A maioria dos alunos chegou hoje.

If English uses most people in a very general sense, Portuguese may use a different structure depending on context. But for this sentence, a maioria is completely natural.