Hey Sven, having the exact same issue my end - I want to use the latest version of the packages and apollo client 3 - will report back if I get anywhere.
Edit: So with the latest versions of both apollo client and codegen-cli/introspection/fragment-matcher I get the correct schema output if I just add the following to my codegen.yml.
config: apolloClientVersion: 2
I’m going to test this as part of my build using it to hydrate from NuxtServerInit inside of Vuex. Will post another update if I see anything other than the Unions and __schema required for DynamicZones