I'm seeing a warning message while trying to use this module with a smart date field in a layout for an entire content type. (I'm not sure the layout builder context is relevant, but I'm mentioning it just in case.) The warning goes away if I check the box for "Show Add to Cal widget for past events?"
Warning: Undefined array key "past_events" in Drupal\addtocal_augment\Plugin\DateAugmenter\AddToCal->configurationFields() (line 427 of modules/contrib/addtocal_augment/src/Plugin/DateAugmenter/AddToCal.php).
Drupal\addtocal_augment\Plugin\DateAugmenter\AddToCal->configurationFields(Array, Array, Object) (Line: 157)
date_augmenter_make_config_fields(Array, Array, Object, Object) (Line: 49)
date_augmenter_field_formatter_third_party_settings_form(Object, Object, '_custom', Array, Object) (Line: 318)
Drupal\layout_builder\Plugin\Block\FieldBlock->Drupal\layout_builder\Plugin\Block\{closure}(Object, 'date_augmenter') (Line: 395)
Drupal\Core\Extension\ModuleHandler->invokeAllWith('field_formatter_third_party_settings_form', Object) (Line: 324)
Drupal\layout_builder\Plugin\Block\FieldBlock->thirdPartySettingsForm(Object, Object, Array, Object) (Line: 284)
Drupal\layout_builder\Plugin\Block\FieldBlock->formatterSettingsProcessCallback(Array, Object, Array)
call_user_func_array(Array, Array) (Line: 1006)
Drupal\Core\Form\FormBuilder->doBuildForm('layout_builder_update_block', Array, Object) (Line: 1069)
Drupal\Core\Form\FormBuilder->doBuildForm('layout_builder_update_block', Array, Object) (Line: 1069)
Drupal\Core\Form\FormBuilder->doBuildForm('layout_builder_update_block', Array, Object) (Line: 579)
Drupal\Core\Form\FormBuilder->processForm('layout_builder_update_block', Array, Object) (Line: 326)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 73)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 638)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 181)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 53)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 741)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)