getIntrospectionQuery only requests the name field from the root queryType object
(https://github.com/graphql/graphql-js/blob/6e48d16f92b9a6df8638b1486354c6be2537033b/src/utilities/getIntrospectionQuery.ts)

queryType { name }

yet the IntrospectionQuery datatype defines queryType as IntrospectionNamedTypeRef (https://github.com/graphql/graphql-js/blob/main/src/utilities/getIntrospectionQuery.ts#L167) which requires kind as well

export interface IntrospectionNamedTypeRef<
  T extends IntrospectionType = IntrospectionType,
> {
  readonly kind: T['kind'];
  readonly name: string;
}

This means that copying the result of the querying a GQL API with the introspection query as JSON and trying to assign to IntrospectionQuery will fail with:

The types of '__schema.queryType' are incompatible between these types.
Property 'kind' is missing in type '{ name: string; }' but required in type 'IntrospectionNamedTypeRef'.