Browsers don't speak grpc natively. There is a separate spec for browser support, but it's a very new project https://github.com/grpc/grpc-web/blob/master/README.md

OP here. We considered this, but decided against it for a couple reasons.

First and foremost our customers universally favor REST APIs. GraphQL and gRPC are better tech wise but REST is more familiar.

Next gRPC uses pure HTTP/2 which doesn’t work with an AWS ALB.

Thanks to the grpc ecosystem the HTTP/1 and REST transcoding is just an Envoy config.