GraphQL is the new mongodb. This fancy new thing that people want to use and makes no sense in reality and just causes more problems than it solves. It solves a very specific problem that makes sense at Facebook. It makes 0 sense for companies that have a web app or web and mobile app. And nothing else. Anyone deciding to use graphql is making a dumb decision.
I sometimes have to write integrations with external data providers (most of them being government agencies), and they love graphql, where (IMHO) it makes a lot of sense. They provide data about some entity¹ split into X fields, your application needs maybe 20% of them, and thanks to graphql you don't have to request anything but those 20%. When loading hundreds of millions of records, it saves you from loading, parsing, and then throwing away gigabytes of unnecessary JSON.
1: one example being tax records with all associated information about tax collecting agencies and taxpayers — it's a lot of data
Facebook does not really use GraphQL in their public apps. The apps call named queries defined server side, so GraphQL is just a glorified RPC mechanism, not a query language.
