GraphQL with ApolloServer says "GET query missing." even though I have playground set to true the way another post advised

Question

I am trying to use Postman to hit a graphQL endpoint to teach myself how it works. I have a database with user data prepopulated and two Postman routes that should work but don't work.

The requests I am trying to send via Postman:

(1) Using GraphQL mode under the Body tab

{
  User {
    first_name
    last_name
  }
}

(2) using the raw mode under the Body tab

{
    user {
        first_name
        last_name
    }
}

In both cases I have correctly set the headers Content-Type to application/graphql. So it's not that.

I found two posts about this while Googling. Both are on StackOverflow.

(1) apollo-server returning GET query missing when playground is disabled

This one says basically, "do this":

const server = new ApolloServer({
    introspection: true, // i inserted this line & the next one as specified
    playground: true,
    typeDefs,
    resolvers,
})

(2) GET query missing: Implementing GraphQL Using Apollo On an Express Server

This one references the prior link. It's also for graph-server-express, and I'm using apollo-server-fastify

I also found Apollo Graphql with Fastify who also has "GET query missing." issue but no solution. It says to downgrade to fastify v2 but that's an old answer from 2020. This is 2022, we can do better.

Again the issue is that Postman says "GET query missing." to all my requests.

My server:

async function startApolloServer(typeDefs, resolvers) {
  const apolloServer = new ApolloServer({
    // introspection: true,
    // playground: true, // to resolve "GET query missing." in Postman
    typeDefs,
    resolvers,

    plugins: [
      fastifyAppClosePlugin(fastify),
      ApolloServerPluginDrainHttpServer({ httpServer: fastify.server }),
      ApolloServerPluginLandingPageGraphQLPlayground(),
    ],
    context: ({ request, reply }) => {
      //Invaluable for debugging
      if (env === "development") {
        console.log("GOT A REQUEST: ", request.body);
      }
      return { knex, reply };
    },
  });

  await apolloServer.start();
  fastify
    .register(helmet)
    .register(require("fastify-sensible"))
    .register(require("fastify-healthcheck"))
    .register(require("fastify-formbody"))
    .register(apolloServer.createHandler());

  await fastify.listen(serviceListeningPort);
  console.log(
    ` Server ready at http://localhost:${serviceListeningPort}${apolloServer.graphqlPath}`
  );
}

startApolloServer(typeDefs, resolvers);

Also, the updated version of Apollo Server seems to replace playground: true with ApolloServerPluginLandingPageGraphQLPlayground(), which for me enables a page that says "Loading GraphQL Playground" at the server root but never finishes loading.