@id and nquad in the playground

Hi All

I'm trying two formats in the playground: [1]

{
  "@context": {
    "@vocab": "urn:solid:"
  },
  "bookmarks": [
    {
      "id": "#1751229072.422",
      "@type": "Bookmark",
      "url": "https://markbook.org/",
      "title": "Markbook",
      "tags": [],
      "created": 1751229072,
      "updated": 1751229072,
      "isFavorite": 1,
      "isArchived": 0
    }
  ]
}

This first one works

but when I change id -> @id all the nquads disappear?

Is this a JSON-LD thing or a playground issue?

Thanks in advance
Melvin

[1]
https://json-ld.org/playground/#startTab=tab-nquads&json-ld=%7B%22%40context%22%3A%7B%22%40vocab%22%3A%22urn%3Asolid%3A%22%7D%2C%22bookmarks%22%3A%5B%7B%22id%22%3A%22%231751229072.422%22%2C%22%40type%22%3A%22Bookmark%22%2C%22url%22%3A%22https%3A%2F%2Fmarkbook.org%2F%22%2C%22title%22%3A%22Markbook%22%2C%22tags%22%3A%5B%5D%2C%22created%22%3A1751229072%2C%22updated%22%3A1751229072%2C%22isFavorite%22%3A1%2C%22isArchived%22%3A0%7D%5D%7D&frame=%7B%7D&context=%7B%7D