How do i fetch a content relationship in a group with all the data

Yes, but you will need to to get the linked documents info. GraphQuery is not GraphQL. GraphQuery uses a GraphQL-like syntax. However, GraphQuery doesn’t include some GraphQL features such as named queries or introspection.

You might query like this then:

import * as prismic from "@prismicio/client"

const client = prismic.createClient("example-prismic-repo")

async function init() {
  const response = await client.getAllByType("blog", {
    graphQuery: `{
      blog {
        author_link {
          ...on author {
            author_name
          }
        }
      }
    }`
  })

  return response
}

init()