JSFiddle - React, Tailwind, and code Playground

HTML

<p>
  <select id="ddSelectFields" onchange="dd_change()">
    <option value="">Feld wählen</option>
    <option value="EingabeFeld1">EingabeFeld1</option>
    <option value="EingabeFeld2">EingabeFeld2</option>
    <option value="EingabeFeld3">EingabeFeld3</option>
    <option value="EingabeFeld4">EingabeFeld4</option>
  </select>
</p>
<div id="FieldGroup1">
<div class="hidden" id="EingabeFeld1">
  <label for="sel1">EingabeFeld1</label>
  <input type="text" id="sel1" />
</div>
<div class="hidden" id="EingabeFeld2">
  <label for="sel2">EingabeFeld2</label>
  <input type="text" id="sel2" />
</div>

<div class="hidden" id="EingabeFeld3">
  <label for="sel3">EingabeFeld3</label>
  <input type="text" id="sel3" />
</div>

<div class="hidden" id="EingabeFeld4">
  <label for="sel4">EingabeFeld4</label>
  <input type="text" id="sel4"  />
</div>
</div>

CSS

.hidden { display: none; }
.visible { display: block; }

JavaScript

function dd_change(){
	var dd = document.getElementById('ddSelectFields');
	var selectedField = dd.options[dd.selectedIndex].value;
  var allfields = document.querySelectorAll('div#FieldGroup1 div');
  allfields.forEach(function(el){
    el.className = (el.id == selectedField) ? "visible" : "hidden";
  });
}