I'm about to begin working on an API, for which I plan to add GraphQL connectivity for processing data. The data processed will mainly be audio files being downloaded/uploaded with some user messaging & authentication.

I don't mind the difficulty in any service since I've used C++ (for data structures & algorithms at least) and would also say I am patient and can learn fairly quickly. My main concerns would be their performance, libraries/community, and job marketability.

Why I'm stuck between these three...

Symfony: I've programmed in PHP for back-end in a previous internship and may do so again in a few months.

Node.js: It's newer than PHP, and it's JavaScript where my front-end stack will be React and (likely) React Native.

Golang: It's newer than PHP, I've heard of its good performance, and it would be nice to learn a new (growing) language.

I personally like using a wholly JS stack, with TypeORM + MySql/Postgres over MongoDb + Mongoose because TypeOrm's Typescript support is much stronger. After developing large projects with Typescript, there is no going back to regular javascript (typings help catch a LOT of errors / maintains data structure !)

Sticking with a javascript stack will allow you to share certain aspects of your application between front and backend. For example: one particularly common feature is to validate API call data and form entry data. Both of these are the same data shape typically (aside from pagination, metadata, etc), and can benefit from a single schema for validation. I use Yup to define this schema, then in the front and back end I can utilize this definition instead of rewriting the same logic in two different languages.

Same goes for certain utility functions such as data structure typings, decryption, encryption, sanitizing inputs, formatting of data, and other utilities. No point of writing these in two languages when both frontend and backend will use them. It will also help reduce developer work load, due to less tests / code to work with.

The only thing you must ensure in your import chain the frontend never imports any secret variables or sensitive logic used by the backend, as that will get bundled into your application. All shared imports should be individual modules

If you want to go one step further, next.js is basically create react app with server side rendering (SSR). This would allow you to skip the annoying step of configuring separate backend and frontend build tools. Might be worth exploring depending on your skill level.

In my humble opinion the best available php platform is "API Platform". I have tried a lot of backend frameworks in the last 10 years, and that is one of the best, at least in the PHP ecosystem. It's based on Symfony, it supports plenty of features like Swagger docs, Rest API, GraphQL. You can plugin React Admin to have a full admin in no time. But the best part in my opinion it's how you can easily extend the backend taking advantage of the ORM Doctrine (which is one of the most mature available across all technologies) and all the plugins of Symfony. The fact that the Doctrine entities are in automatic relation and they can be exposed as GraphQL it's a big win if you have a complex database. It is also possible to reverse engineering an existing database and create automatically all the entities, admin, restapi, graphql endpoints ... welcome to the future :)