Why would this make any sense?

    const myDiv = div(
      {id: 'container', className: 'my-class'}, 
      h1('Hello World'), 
      p('This is a dynamically generated paragraph.')
    );
    document.body.appendChild(myDiv);

That's completely unnecessary these days with template strings. It's gonna be much faster as well to use browser's native parsing.

    const div = document.createElement('div');
    let text = 'This is a dynamically generated paragraph';
    
    div.innerHTML = `
      <div id="container" class="my-class">
        <h1>Hello world</h1>
        <p>${text}</p>
      </div>
    `;
    document.body.append(...div.children);

Keep it simple!