<?php

$bodyBlocks = [];
foreach ($page->body()->toBlocks() as $block) {
  if ($block->type() === 'text') {
    $bodyBlocks[] = [
      'type' => 'text',
      'html' => $block->content()->text()->value(),
    ];
  }
}

$specificData = [
  'backgroundImage' => $page->backgroundImage()->toFile()?->url(),
  'body'            => $bodyBlocks,
];

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

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