https://understanddrupal.com/articles/migrating-google-sheets-drupal

google_sheets_json_sample.json

{
  "feed": {
    "entry": [
      {
        "gsx$uniqueid": {
          "$t": "1"
        },
        "gsx$name": {
          "$t": "One Uno Un"
        },
        "gsx$photo-file": {
          "$t": "P01"
        },
        "gsx$bookref": {
          "$t": "B10"
        }
      }
    ]
  }
}

node_migration_process_destination_and_dependencies.yml

process:
  field_ud_image/target_id:
    plugin: migration_lookup
    migration: udm_microsoft_excel_source_image
    source: src_photo_file
destination:
  plugin: 'entity:node'
  default_bundle: ud_paragraphs
migration_dependencies:
  required:
    - udm_microsoft_excel_source_image
    - udm_libreoffice_calc_source_paragraph
  optional: []

node_migration_source.yml

source:
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: google_sheets
  urls: 'http://spreadsheets.google.com/feeds/list/1YVJt9isPNjkUNHf3YgoTx38r04TwqRYnp1LFrik3TAk/1/public/values?alt=json'
  fields:
    - name: src_unique_id
      label: 'Unique ID'
      selector: uniqueid
    - name: src_name
      label: 'Name'
      selector: name
    - name: src_photo_file
      label: 'Photo ID'
      selector: photo-file
    - name: src_book_ref
      label: 'Book paragraph ID'
      selector: bookref
  ids:
    src_unique_id:
      type: integer