rootpage.php

    protected function getRootPage($uid)
    {
        /** @var PageRepository $pageRepository */
        $pageRepository = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(PageRepository::class);
        $rootLinePages = $pageRepository->getRootLine($uid);
        $rootPage = null;
        foreach ($rootLinePages as $page) {
            if ($page['is_siteroot'] === '1') {
                $rootPage = $page;
                break;
            }
        }
        return $rootPage;
    }