Hi Sefi18,
This error occurs when the federated supergraph contains more than one Query operation.
Extending the root operations (Query, Mutation, Subscription) is necessary. The open-source tests for federation are available here, and you’ll notice “extend type Query” appears quite frequently. If you’ve seen contradicting information, please do send it over to me.
With some luck, this above might solve your problem. If not, please don’t hesitate to @ me, and we’ll take it from there.
David