Thank you for your reference, we've not had the plan to integrate WPGraphQL with Meta Box on the roadmap yet. But a user has created a integration plugin to use WPGraphQL and Meta Box, you can try to use his plugin to build your site. https://github.com/hsimah/wp-graphql-metabox/
Hi, we're building headless WordPress too with Gtasby and an official WPGraphQL integration would be very important. We can't rely on temporary solutions built by random users. Please consider adding support to WPGraphQL. Other popular (and even new) custom field builders have support to it out of the box.