video-list.tsx

type Video = {
  title: string
  duration: number
  coverUrl: string
}

type Props = {
  items: Array<Video>
}

const VideoList = ({ items }) => {
  return (
    <ul>
      {items.map(item => 
        <Thumbnail 
          key={item.title} 
          video={item} 
        />
      )}
    </ul>
  )
}

I guess this needs Props to be referenced to explain what you wanted here.

type Video = {
  title: string
  duration: number
  coverUrl: string
}

type Props = {
  items: Array<Video>
}

const VideoList = ({ items } : Props) => {
  return (
    <ul>
      {items.map(item => 
        <Thumbnail 
          key={item.title} 
          video={item} 
        />
      )}
    </ul>
  )
}