When specifying disabled on an option, the rendered result doesn't have the disabled attribute on the option. The option is still able to be selected and still triggers the input event.

Rendered result of example fiddle:

<select class="custom-select" calss="mb-3">
  <option value="">Please select some item</option>
  <option value="a">This is First option</option>
  <option value="b">Default Selected Option</option>
  <option value="c">This is another option</option>
  <option value="d">This one is disabled</option>
</select>

The last option in this example should have the disabled attribute set. (disabled="true" or disabled="disabled")

Also note class has a typo of calss in the example fiddle