JSFiddle - React, Tailwind, and code Playground

HTML

<div class="quest-alternatives">
<p class="brand-alternative">
<span class="brand-id hidden" style="display: none;">123</span>
<span class="radio-button" id="brand-0"></span>
<label for="brand-0" class="brand-name">Opção 0</label></p>

<p class="brand-alternative">
<span class="brand-id hidden" style="display: none;">456</span>
<span class="radio-button" id="brand-1"></span>
<label for="brand-1" class="brand-name">Opção 1</label></p>

<p class="brand-alternative">
<span class="brand-id hidden" style="display: none;">789</span>
<span class="radio-button" id="brand-2"></span>
<label for="brand-2" class="brand-name">Opção 2</label></p></div>

JavaScript

var x = $('span.brand-id.hidden').map(function() {
    return $(this).html();
});

console.log(x);