module

<?php

use Drupal\Component\Utility\Html;
use Drupal\Core\Form\FormStateInterface;


/**
 * Implements hook_form_FORM_ID_alter() for 'views_exposed_form'.
 */
function hook_form_views_exposed_form_alter(&$form, FormStateInterface $form_state) {
  // Configure the values to your needs.
  $view_name = 'my_view';
  $display_name = 'my_display';
  $entity_type_id = 'taxonomy_term';
  $reference_field = 'field_category';
  // The field on the referenced entity.
  $flag_on_reference_field = 'field_hide_on_exposed_form';

  if ($form['#id'] == Html::getId("views-exposed-form-{$view_name}-{$display_name}")) {
    $entity_storage = \Drupal::entityTypeManager()->getStorage($entity_type_id);
    $options = &$form[$reference_field]['#options'];
    foreach ($entity_storage->loadMultiple(array_keys($options)) as $id => $entity) {
      if ($entity->hasField($flag_on_reference_field) && !$entity->{$flag_on_reference_field}->isEmpty()) {
        unset($options[$id]);
      }
    }
  }
}

// Assume $entity is your translatable entity object.
$default_language_entity = $entity->getUntranslated();
$default_language_code = $default_language_entity->language()->getId();

/**
 * Implements hook_tokens().
 */
function example_group_tokens($type, $tokens, array $data, array $options, BubbleableMetadata $bubbleable_metadata) {
  $replacements = [];

  // Automatically expose related entities to group_relationships.
  if ($type == 'group_relationship' && !empty($data[$type])) {
    $token_service = \Drupal::token();

    /** @var \Drupal\example\GroupRelationshipTypeServiceInterface $group_relationship_type_service */
    $group_relationship_type_service = \Drupal::service('example.group_relationship_type_service');

    $group_relationship = $data['group_relationship'];
    assert($group_relationship instanceof GroupRelationshipInterface);

    foreach ($tokens as $name => $original) {
      /** @var \Drupal\Core\Entity\EntityTypeInterface $entity_type */
      foreach ($group_relationship_type_service->getConfiguredEntityTypes() as $entity_type_id => $entity_type) {
        if ($name == $entity_type_id) {
          $entity = $group_relationship->getEntity();
          $bubbleable_metadata->addCacheableDependency($entity);
          $replacements[$original] = $entity->label();
        }

        // Actual chaining of tokens handled below.
        if ($entity_tokens = $token_service->findWithPrefix($tokens, $entity_type_id)) {
          $replacements += $token_service->generate($entity_type_id, $entity_tokens, [$entity_type_id => $group_relationship->getEntity()], $options, $bubbleable_metadata);
        }
      }
    }
  }

  return $replacements;
}

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Replace ugly "Field cannot be empty" error message for comments.
 */
function meta_base_form_comment_story_comment_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  array_unshift($form['#validate'], '_meta_base_comment_validate');
  $form['comment_body']['widget']['#required'] = false;
  $form['comment_body']['widget'][0]['#required'] = false;
}

/**
 * Custom validation for better error message on empty comments.
 */
function _meta_base_comment_validate(&$form, \Drupal\Core\Form\FormStateInterface $form_state) {
  if (empty($form_state->getValue('comment_body')[0]['value'])) {
    $form_state->setErrorByName('comment_body', t('Please enter a comment. An empty comment cannot be saved.'));
  }
}

/**
 * Implements hook_theme_registry_alter().
 */
function hook_theme_registry_alter(&$theme_registry) {
  // Kill the gin breadcrumb preprocessor, since we do our own backend
  // breadcrumb logic.
  foreach ($theme_registry['breadcrumb']['preprocess functions'] as $key => $value) {
    if ($value == 'gin_preprocess_breadcrumb') {
      unset($theme_registry['breadcrumb']['preprocess functions'][$key]);
    }
  }
}

// Get DrupalDateTime object with current date & time (timezone from system is used).
$current_date = new DrupalDateTime();

// Get DrupalDateTime object with the value from a field of type date (timezone from system is used).
$deadline = $entity->field_date->date;

// Change timezone to 'UTC' (just for demo/devbit purpose).
$freelancer_dl->setTimezone(new DateTimeZone('UTC'));
$current_date->setTimezone(new DateTimeZone('UTC'));

// Format DrupalDateTime object (just for demo/devbit purpose).
$freelancer_dl->format(\Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATETIME_STORAGE_FORMAT);
$current_date->format(\Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATETIME_STORAGE_FORMAT);

// Modify DrupalDateTime object.
$deadline->modify('-2 Days');

// You can compare the DrupalDateTime objects.
if ($deadline <= $current_date) {
  //...do something...
}