I discovered that Symfony StreamedResponse is not sent to the client in chunks, but only all data at once.
See https://github.com/Baldinof/roadrunner-bundle/blob/3.x/src/RoadRunnerBridge/HttpFoundationWorker.php#L46
But RoadRunner supports this feature https://docs.roadrunner.dev/docs/http/resp-streaming

Proposal is to forward chunk-data iterator from Symfony to Roadrunner, thanks