On type

When there are multiples types available, you need to use ... on TYPE. Some options here from the explorer are Commit, Tree, Blob and Tag.

Example:

{
  repository(owner: "michaelcurrin", name: "aggre-git") {
    defaultBranchRef {
      target {
        ... on Commit {
          history(first: 3) {
            edges {
              node {
                committedDate
              }
            }
          }
        }
      }
    }
  }
}