storm-1.x-dev/modules/storm_blocks/modules/storm_block_accordion/storm_block_accordion.module

<?php

/**
 * @file
 * Provides an Accordion block component.
 */

use Drupal\block_content\BlockContentInterface;

/**
 * Implements hook_theme_registry_alter().
 */
function storm_block_accordion_theme_registry_alter(&$theme_registry) {
  $module_path = \Drupal::service('extension.list.module')->getPath('storm_block_accordion');

  $base_hooks = [
    'field' => [
      'registry' => 'field__block_content__field_accordion_items__accordion',
      'template' => 'field--block-content--field-accordion-items--accordion',
    ],
    'paragraph' => [
      'registry' => 'paragraph__accordion_item__default',
      'template' => 'paragraph--accordion-item--default',
    ],
    'block' => [
      'registry' => 'block__accordion',
      'template' => 'block--accordion',
    ],
  ];

  foreach ($base_hooks as $base_hook => $theme) {
    $theme_registry[$theme['registry']] = [
      'path' => $module_path . '/templates',
      'template' => $theme['template'],
      'render element' => $theme_registry[$base_hook]['render element'],
      'base hook' => $base_hook,
      'type' => 'module',
      'theme path' => $module_path,
      'preprocess functions' => $theme_registry[$base_hook]['preprocess functions'],
    ];
  }
}

/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function storm_block_accordion_theme_suggestions_block_alter(array &$suggestions, array $variables) {
   $element = $variables['elements'];
  // Block suggestions for custom block bundles.
  if (isset($element['content']['#block_content'])) {
    array_splice($suggestions, 1, 0, 'block__' . $element['content']['#block_content']->bundle());
  }
}