Hi @Bevaldss,
from the .NET Agent's perspective I can tell that there is no specific instrumentation for graphql-dotnet/graphql-client, but the agent would still recognise those calls as an outgoing HTTP call, so you'd see those in the Dependency view.
Overall to me this seems more like either an issue in Kibana or in Elasticsearch. I say this based on the fact that you say that "We do have good data in Service Map, Services, Traces, Transactions.". If you see the outgoing HTTP calls to the GraphQL service, then the same data would be used to populate the dependencies view.
Which logs should I look for here, in this case of troubleshooting? Any hints are appreciated.
I think Kibana logs would help here as the first step - and then I'd ask people from the APM UI team to look at it.
I'd also note that the APM .NET Agent version 1.8.0 is a bit old now, we had multiple releases since then, but I don't think it'd change much on this specific issue if you'd update to the latest Agent version.