How do I save as draft in strapi?

The way that I found to do that is just passing the property published_at as null when perform the mutation.

published_at is a default property that strapi assign to each collection.

For the query

mutation CreateRecord (
  $recordName: String!,
  $published_at: DateTime
) {
  createComment (input: {
    data : {
      recordName: $recordName,
      published_at: $published_at
    }
  })
}

and when is time to send the values

createRecords({
  variables: {
    recordName: "I am a new record saved as draft"
    published_at: null
  }
});

What version of Strapi are you using?

The Draft & Publish feature has been released recently. You should definitely give it a try: https://strapi.io/blog/announcing-a-new-draft-and-publish-feature