Alter Paragraphs form and apply conditional form fields - Drupal 10.3.x

custom.module

<?php
// https://www.drupal.org/docs/drupal-apis/form-api/conditional-form-fields#s-table-of-contents
/**
 * Implements hook_field_widget_single_element_[WIDGET_TYPE]_form_alter().
 */
function custom_field_widget_single_element_paragraphs_form_alter(&$element, &$form_state, $context) {
     /** @var \Drupal\field\Entity\FieldConfig $field_definition */
  $field_definition = $context['items']->getFieldDefinition();
  $paragraph_entity_reference_field_name = $field_definition->getName();

  if ($paragraph_entity_reference_field_name == 'field_product_details') {
        /** @see \Drupal\paragraphs\Plugin\Field\FieldWidget\ParagraphsWidget::formElement() */
        $widget_state = \Drupal\Core\Field\WidgetBase::getWidgetState($element['#field_parents'], $paragraph_entity_reference_field_name, $form_state);

        /** @var \Drupal\paragraphs\Entity\Paragraph $paragraph */
        $paragraph_instance = $widget_state['paragraphs'][$element['#delta']]['entity'];
        $paragraph_type = $paragraph_instance->bundle();

        // Determine which paragraph type is being embedded.
        if ($paragraph_type == 'product_details') {
        $dependee_field_name = 'field_new_select_list';
        $selector = sprintf('select[name="%s[%d][subform][%s]"]', $paragraph_entity_reference_field_name, $element['#delta'], $dependee_field_name);
        // Dependent fields.
        $element['subform']['field_product_category_other']['#states'] = [
            'visible' => [
                $selector => ['value' => 'yed'],
            ],
        ];
        }
    }
  }
 ?>