Symfony API Platform boils to ORM-generated SQL via Doctrine, which is verbose, but not overly clever. So the only link I could give you there would be to the Doctrine query builder docs (I won't subject you to API Platform's docs). I imagine a more sophisticated graphql dialect like what Prisma supports can generate some pretty gnarly sql, but that's ORMs for you. But exposing your data model directly through graphql is also not recommended, same with REST APIs (I can't claim the high ground, my biggest graphql project exposes models directly. The tradeoff was worth it in this case). So in the end you're writing custom controllers/resolvers anyway, and field resolvers are where graphql really starts to shine.

Typically libraries use a Dataloader + ORM to implement this which gets you pretty far, outside of that some libs like Strawberry with automatically optimize your queries for you if you return Django ORM Querysets.

Any query you were going to build and serve with Rest can be made with these two methods or even a raw dataloader and manual SQL string.

Every GQL implementation I have seen explicitly has a way to avoid n+1 queries.