world-game/site/templates/game.json.php

<?php

$specificData = [
  'description' => $page->description()->value(),
  'rules' => $page->rules()->toBlocks(),
  'gameStatus' => $page->gameStatus()->value(),
  'isEmbedded' => $page->isEmbedded()->toBool(),
  'playLink' => $page->playLink()->value(),
  'cover' => $page->cover()->toFile()?->url(),
  'parentUrl' => $page->parent()->url()
];

$pageData = array_merge($genericData, $specificData);

header('Content-Type: application/json');
echo json_encode($pageData);