Finding search results in custom fields

Question

How does Wordpress search in custom fields?

I researched and saw that his search works using the title and content of the content. I created a project that uses custom fields, such as: address and phone number, with the possibility of the user to enter the city name, address, state or telephone.

The city name is the normal title, the rest of the fields are all custom.

I am using a query to do this, because I am displaying the result via ajax

$string = $_GET['string'];
$argumentos = [
    'post_type' => 'unidade',
    'posts_per_page' => -1,
    's' => $string
];
$posts = new WP_Query($argumentos);
?>