How to query the featured image for a video? (attachment)

[ShahriarKh]

I can't find the required node to get the featured image of an attachment. The screenshot above is basically an mp4 video uploaded to the media library + an image (tree) set as its featured image.

I'm looking for something like featuredImage in posts, so I can query it like:

query NewQuery {
  mediaItem(id: "1201", idType: DATABASE_ID) {
    mediaItemUrl # this works, and returns the video file URL 
    featuredImage { # I can't find this (or something similar) to get the image file URL 
        node {
            mediaItemUrl
        }
    }
  }
}

Is it even implemented? If not, how can I add it... maybe with a plugin?