Element without explicit #access => TRUE is removed by \Drupal\webform\Plugin\WebformElementBase::setConfigurationFormDefaultValueRecursive()

For the record, the same code works as expected without an explicit '#access' => TRUE, in a Webform handler's form builder, like \Drupal\foo\Plugin\WebformHandler\Foo::buildConfigurationForm().

Yes, in a Webform element, a property needs to be included via ::defineDefaultProperties to have #access automatically set to TRUE. Otherwise, you must explicitly set an element on the element edit form #access to TRUE.

We can't change this behavior.

Ack, thanks for the clarification.