Frontend Category Checkbox

Your select tag doesn’t have a name attribute, it only has a type and value. The name is used as an ID when you POST most likely the reason your data isn’t saving.

Quick Example:

<form action="/action_page.php">
<select name="cars">
  <option value="volvo">Volvo XC90</option>
  <option value="saab">Saab 95</option>
  <option value="mercedes">Mercedes SLK</option>
  <option value="audi">Audi TT</option>
</select>
<input type="submit" value="Submit">
</form>

<p>Choose a car, and click the "Submit" button to send input to the server.</p>

</body>
</html>

You can run this example here -> Run Example