$wgarticletocategory2ConfigBlacklist = true; is not working by default. To make it work again the following workaround should be good enough:
- The flag in LocalSettings.pgp is actually camelcased. Change it to
$wgArticleToCategory2ConfigBlacklist = true;
- The extension than uses a hook that is long depreciated and leading to a error on every category page (Info). Therefore go to line 40 in ArticleToCategory2.hooks.php and change
$content = $rev->getText();
$content = ContentHandler::getContentText($rev->getContent());
Afterwords everthing should be working fine.