How to get last user with wpdb?

If you’re trying to get the last user created with the username format usuario*, I’d recommend using get_users() instead of writing a SQL query.

$args = array(
    "search"         => "usuario*",            // Search string
    "search_columns" => array( "user_login" ), // Field(s) to search
    "order"          => "DESC",                // Search order
    "orderby"        => "user_registered",     // Order by this
    "number"         => 1,                     // Get only this many users
);
$user_objects = get_users( $args );
// Ensure we've got results
if ( ! empty( $user_objects ) ) {
    // Pull the 1st array element, which will be a WP_User object,
    // and use the get() method to extract the username to a variable
    $most_recent_usuario = $user_objects[0]->get( 'login_name' );
}
echo "<p>O último usuário é {$most_recent_usuario}</p>";

References

• get_users()
• WP_User_Query::prepare_query() for the $args details
• WP_User::get() to extract the user_login from the WP_User object