In the docs, I found that I could use a custom hook for this – so I added the fol

$GLOBALS['TYPO3_CONF_VARS']['EXT']['news']['Domain/Repository/AbstractDemandedRepository.php']['findDemanded'][$_EXTKEY] = \REDACTED\NewsExtended\Hooks\Repository::class . '->modify';

And in the Repository.php:

namespace REDACTED\NewsExtended\Hooks;

use TYPO3\CMS\Core\Utility\GeneralUtility;
use \GeorgRinger\News\Domain\Repository\NewsRepository;

class Repository
{
    public function modify(array $params, NewsRepository $newsRepository)
    {
        $this->updateConstraints($params['demand'], $params['respectEnableFields'], $params['query'], $params['constraints']);
    }

    /**
     * @param \GeorgRinger\News\Domain\Model\Dto\NewsDemand $demand
     * @param bool $respectEnableFields
     * @param \TYPO3\CMS\Extbase\Persistence\QueryInterface $query
     * @param array $constraints
     */
    protected function updateConstraints($demand, $respectEnableFields, \TYPO3\CMS\Extbase\Persistence\QueryInterface $query, array &$constraints)
    {
        //$constraints[] = $query->like('title', '%' . $subject . '%');
        //$constraints[] = $query->equals('related', 0);
        //echo $query->matching($query->contains('likedPosts', $post))->count();    
    }
}

I’m having trouble setting constraints here. I want to filter, so in all places, news that have relatedfrom set, are not shown. For some reason, relatedfrom is empty in the database, but in TYPO3 I can freely loop through it.
I’ve through about just using javascript and remove them, but that would break pagination.

Do I have to build a custom controller? If yes – I can’t find any way, how I could just “extend” the existing one (e.g. the extended controller would just call the paren’t methods and modify the output if required).