When I edit a script and browse for attachment thumbnails, the editor marks the syntax .thumbnails as an error.

Property 'thumbnails' does not exist on type '{ readonly id: string; readonly url: string; readonly filename: string; readonly size?: number; readonly type?: string; readonly thumbnail?: {

The autocomplete suggests .thumbnail (no s). It’s a bug: this wrong syntax fails at runtime, but is considered as the correct one by the script editor.