JSFiddle - React, Tailwind, and code Playground

HTML

<select id="selectField1" style="padding-left: 20px;width:150px">
        <option value="option0">-Bitte auswählen-</option>
        <option value="option1">Menü 1</option>
        <option value="option2">Menü 2</option> 
		<option value="option3">Menü 3</option> 
    </select>


<div id="option1" class="block">
	<select id="selectField2" style="padding-left: 20px;width:150px">
	        <option value="option0">-Bitte auswählen-</option>
			<option value="option1-1">1.1</option>
			<option value="option1-2">1.2</option> 
			<option value="option1-3">1.3</option> 
	</select>
</div>

<div id="option2" class="block">
	<select id="selectField2" style="padding-left: 20px;width:150px">
			<option value="option2-1">2.1</option>
			<option value="option2-2">2.2</option> 
			<option value="option2-3">2.3</option> 
	</select>
</div>

<div id="option3" class="block">
	<select id="selectField2" style="padding-left: 20px;width:150px">
			<option value="option3-1">3.1</option>
			<option value="option3-2">3.2</option> 
			<option value="option3-3">3.3</option> 
	</select>
</div>


<div id="option1-1" class="block">[custom_field1] -> Inhalt von Custom Field1.</div>
<div id="option1-2" class="block">[custom_field1] -> Inhalt von Custom Field2.</div>
<div id="option1-3" class="block">[custom_field1] -> Inhalt von Custom Field3.</div>

JavaScript

$('.block').hide();
$('#selectField1,#selectField2').change(function () {
    $('.block').hide();
    $('#'+$(this).val()).fadeIn();
});