When implementing something like this I indeed prefer to share as much code as possible between client/server.
My daily environment is mostly JVM-based (desktop/android/server) so your project is probably not a great fit for me but I'm definitely going to look into it for some inspiration.
While it is true that you have to duplicate the mutations in the basic setup, you do not have to share the querying/reading code as it lives primarily on the client.
Also, if your backend happens to be javascript/typescript, then you can share the majority of the mutation code between client and server and the result is quite sweet.