Why does this if statement fail when using OR here?

I am trying to hide (form_alter) parts of Webform Elements in webform_ui_elements form.

 $element_type = $form_state->get('element_properties','type')('type');
if (($element_type != 'managed_file') OR ($element_type != 'select')) {
  unset($form('properties')('element')('multiple'));
}

As long as there is no OR and either Type is select oder managed_file like this it works

     $element_type = $form_state->get('element_properties','type')('type');
if (($element_type != 'managed_file') {
  unset($form('properties')('element')('multiple'));
}

As soon, as i start checking for both Types nothing is hidden anymore.

Any hints greatly appreciated!