Error implementing a singleton in Sanity config file

import {defineConfig} from 'sanity'
import {deskTool} from 'sanity/desk'
import {StructureBuilder} from 'sanity/desk'

const myStructure = (S: StructureBuilder) =>
  S.list()
    .title('Base')
    .items([
      S.listItem()
        .title('Site Settings')
        .child(S.document().schemaType('siteSettings').documentId('siteSettings')),
      ...S.documentTypeListItems(),
    ])

const mySchemaTypes = [
  {
    name: 'siteSettings',
    title: 'Site Settings',
    type: 'document',
    fields: [
      {
        name: 'title',
        title: 'Site Title',
        type: 'string',
      },
      {
        name: 'description',
        title: 'Site Description',
        type: 'text',
      },
    ],
  },
  {
    name: 'posts',
    type: 'document',
    title: 'Posts',
    fields: [
      {name: 'title', type: 'string', title: 'Title'},
      {name: 'slug', type: 'slug', title: 'Slug'},
      {name: 'content', type: 'array', title: 'Content', of: [{type: 'block'}]},
    ],
  },
]

export default defineConfig({
  name: 'default',
  title: 'sanity-11ty',

  projectId: import.meta.env.SANITY_STUDIO_PROJECT_ID,
  dataset: import.meta.env.SANITY_STUDIO_DATASET,

  plugins: [
    deskTool({
      structure: myStructure,
    }),
  ],

  schema: {
    types: mySchemaTypes,
  },
})

List items with same ID found (siteSettings)

...S.documentTypeListItems().filter(listItem => !['siteSettings'].includes(listItem.getId()))

Invalid link. Your link must contain a type.