I did, the same way you would do with a REST API. you specify a format for a field (in my case, the 'where' and 'join' where JSON structures that you passed as parameters)

Then you write the resolvers that parse that. Pretty much as I would expect you to do it in REST.

(mentioned it in another post, I created a no-code tool that did this, for random data and entities created by the user per tenant/app, so I know the issues with GQL, but I can assure you, doing the same with REST was 10 times harder (api started as REST and moved to GQL after 6 months)