Displaying related faqs fails under PHP 7.3

[responseinformationsdesign]

Displaying related under PHP 7.3 results in a TYPO3 exception:

Error
Using $this when not in object context
in <path to webroot>\typo3\sysext\frontend\Classes\Page\PageRepository.php line 1611
at TYPO3\CMS\Frontend\Page\PageRepository::enableFields('tx_irfaq_q')
in <path to webroot>\typo3conf\ext\irfaq\Classes\Controller\FaqController.php line 1170
at Netcreators\Irfaq\Controller\FaqController->addWorkspaceRestriction()
in <path to webroot>\typo3conf\ext\irfaq\Classes\Controller\FaqController.php line 949
at Netcreators\Irfaq\Controller\FaqController->singleView()
in <path to webroot>\typo3conf\ext\irfaq\Classes\Controller\FaqController.php line 131