layout_builder_extra_field_test.module

<?php


/**
 * @file
 * Provides hook implementations for Layout Builder tests.
 */
use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
use Drupal\Core\Entity\EntityInterface;

/**
 * Implements hook_entity_extra_field_info().
 */
function layout_builder_extra_field_test_entity_extra_field_info() {
    $extra['node']['bundle_with_section_field']['display']['layout_builder_extra_field_test'] = [
        'label' => t('New Extra Field'),
        'description' => t('New Extra Field description'),
        'weight' => 0,
    ];
    return $extra;
}

/**
 * Implements hook_entity_node_view().
 */
function layout_builder_extra_field_test_node_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {
    if ($display->getComponent('layout_builder_extra_field_test')) {
        $build['layout_builder_extra_field_test'] = [
            '#markup' => 'A new extra field.',
        ];
    }
}