> What should AWS do -> provide Postgres or similar as a database choice
If you're interested a postgres option you could check out Supabase GraphQL[1] which is based on pg_graphql [2], a native PostgreSQL extension.
You define your schema in SQL (including any indexes you'd like) and it reflects a full GraphQL API. With that stack, the example you gave about filtering for security would use be solved using a Row Level Security [3] policy where the work all occurs on the DB.
While not a part of pg_graphql, using Supabase as a backend also handles Auth [4] & Storage [5] (both OSS) which covers most of the Amplify bases
[1] https://supabase.com/docs/guides/api#graphql-api-overview [2] https://github.com/supabase/pg_graphql [3] https://www.postgresql.org/docs/current/sql-createpolicy.htm... [5] https://supabase.com/docs/guides/auth [5] https://supabase.com/docs/guides/storage