According to this guide id_token should be in the response if scope parameter contains openid, however the same guide says that scope parameter is not supported.
As I've verified no id_token issued with this flow, even if I had set openid scope in Connected Application configuration. If I put request parameter scope, token endpoint throws an error that scope parameter is not supported for this flow, same as guide says.
Is it documentation error or am I missing something? Is it really impossible to get id_token from Salesforce in headless flows, where user(human) is not involved (user-agent and web-server flows require user interactions)?