JSFiddle - React, Tailwind, and code Playground

HTML

<div class="1 2 3 clone_elem">
	<div class="2 5 parent_del_elem">
		<form>
			<input type="text" name="">
			<input type="password" name="">
			<button type="submit" class="">Submit</button>
		</form>
		<button type="submit" class="add">Добавить</button>
	</div>
</div>

JavaScript

addEventListener("click", function (event) {
	if(event.target.matches(".add")) {
		var original = document.querySelector(".clone_elem");
		var cloned = original.cloneNode(true);
		
		var button = document.createElement('button');
		button.textContent = 'Удалить';
		
		cloned.querySelector(".parent_del_elem").appendChild(button);
		original.parentNode.insertBefore(cloned, original.nextSibling);
	}
});