You will need to set the `authentication type` as `empty` for `GraphQL`, through below configuration, when you disable the `identity server` in Sitecore.

```
<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/">
  <sitecore role:require="Standalone or ContentManagement">
    <authoring>
      <graphql>
        <tokenValidator>
          <param desc="authenticationType">
            <patch:delete/>
          </param>
          <param desc="authenticationType"></param>
        </tokenValidator>
      </graphql>
    </authoring>
  </sitecore>
</configuration>
``` 

Be default, there is a config file located at below location that can be used to set `authentication type` to `empty`.

```
App_Config\Include\Examples\Sitecore.GraphQL.IdentityServer.Disabler.config.example
```

Hope this helps!!! Let me know in case you face any issues.