bookmark-pages/Configuration/TCA/Overrides/tt_content.php

<?php
defined('TYPO3') || die('Access denied.');

(function () {

    \TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
        'BookmarksLikesRatings',
        'Bookmarks',
        'Bookmark Pages'
    );

    \TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
        'BookmarksLikesRatings',
        'PersonalBookmarks',
        'Personal bookmarks of a user'
    );


    $GLOBALS['TCA']['tt_content']['types']['list']['subtypes_addlist']['bookmarkslikesratings_bookmarks'] = 'pi_flexform';
    \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPiFlexFormValue(
        'bookmarkslikesratings_bookmarks',
        'FILE:EXT:bookmarks_likes_ratings/Configuration/FlexForms/Bookmarks.xml'
    );

    $GLOBALS['TCA']['tt_content']['types']['list']['subtypes_excludelist']['bookmarkslikesratings_bookmarks'] = 'recursive,select_key,pages';
})();