Hello,
Running GraphQL On App Engine, it seems there is no GCP Documentation that particularly addresses this concern. However, I do believe there are some information over third party sites.
I see this GitHub link[1] for graphql-yoga, which is based on the Apollo Framework. However, it requires Websockets which may not necessarily be available in App Engine Standard but with App Engine Flexible[2]. Hence, I am not sure how useful that would be in your use-case. I believe there are workarounds provided on this Stackoverflow links for App Engine Standard[3].
This article[4] also attempts to provide some pointers but it is important to note that the article used older apollo and Node.JS runtime.
I suggest you likewise taking this question to the Apollo community[4] to discuss it further.
Thanks!