JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset>
  <input type="radio" id="wien-radio" name="Lehrgang" value="gebucht">
  <label for="wien-radio">Wien Lehrgang 1</label>
  
  <input type="checkbox" id="tablet-checkbox" name="Lehrgang" value="gebucht">
  <label for="tablet-checkbox">Tablet</label><br>
  
  <input type="radio" id="salzburg-radio" name="Lehrgang" value="gebucht">
  <label for="salzburg-radio">Salzburg Lehrgang 2</label>
</fieldset>

CSS

#tablet-checkbox, label[for='tablet-checkbox'] {
  display: none;
}

#wien-radio:checked ~ #tablet-checkbox, #wien-radio:checked ~ label[for='tablet-checkbox'] {
  display: inline-block;
}