TypeORM is great and all - but it has its own quirks too and it's not a silver bullet.
In their case they would also maybe run into some issues as TypeORM has some initialization cost (building a model in memory when it first connects to the DB etc), some object mapping costs and other complexities (particularly around efficient query generation).
While there is nothing stopping it from working in a Lambda this would increase initialization time and cost which both matter since this is for a GraphQL API. I think the solution they've selected (Kysely) is probably a better fit.
In their case they would also maybe run into some issues as TypeORM has some initialization cost (building a model in memory when it first connects to the DB etc), some object mapping costs and other complexities (particularly around efficient query generation).
While there is nothing stopping it from working in a Lambda this would increase initialization time and cost which both matter since this is for a GraphQL API. I think the solution they've selected (Kysely) is probably a better fit.