GitHub Projects Beta aka GitHub Projects Next aka GitHub ProjectNext is now known as GitHub ProjectV2 in the API.
It's not immediately obvious how to use the new API, especially if you're coming from the old beta API.
You no longer need to set the HTTP header: GraphQL-Features: projects_next_graphql
.
You still need to add your GitHub personal access token to the Authorization
header, e.g. Authorization: Basic ghp_...