OptionaldescriptionAlt text for the media
Optionalid32 bit integer used as an optional identifier for component
The id field is optional and is used to identify components in the response from an interaction that aren't interactive components. The id must be unique within the message and is generated sequentially if left empty. Generation of ids won't use another id that exists in the message if you have one defined for another component.
A url or attachment
OptionalspoilerWhether the thumbnail should be a spoiler (or blurred out)
The type of the component
A Thumbnail is a content component that is a small image only usable as an accessory in a section. The preview comes from an url or attachment through the unfurled media item structure.
Thumbnails are only available in messages as an accessory in a section.
See
https://discord.com/developers/docs/components/reference#thumbnail