JSFiddle - React, Tailwind, and code Playground

HTML

<button id='botao'>
    Adicione um formulário
</button>

<div id='formulario'>
    <form id='form' action='#'>
        <input type='submit' id='submit'></input>
    </form>
</div>

JavaScript

var sequencia = 0;

var form = document.getElementById('form');
var submit = document.getElementById('submit');

var cria_formulario = function() {
    
    var input = document.createElement('input');
    input.setAttribute('type', 'text');
    input.setAttribute('name', 'entrada[' + sequencia + ']');
    input.setAttribute('value', 'entrada[' + sequencia + ']');
    sequencia += 1;
    
    form.removeChild(submit);
    form.appendChild(input);
    form.appendChild(document.createElement('br'));
    form.appendChild(submit);
};

var botao = document.getElementById('botao');
botao.onclick = function() {
    cria_formulario();
}