is it possible to hide the playground but still can fetch the API?

Yeah, set

playground

to

false

when starting your Graphql server:

server.start(
  {
    port: process.env.NODE_PORT,
    playground: false,
  },
  () => console.log(`Server is running on ${process.env.NODE_PORT}`)
);

More informations & configuration here: https://github.com/prismagraphql/graphql-yoga#startoptions-options-callback-options-options--void----null-promisevoid

Thanks @Gomah!