Target groups for your Application Load Balancers …

Considerations for the gRPC protocol version. The only supported listener protocol is HTTPS. The only supported action type for listener rules is forward. The only supported target types are instance and ip.. The load balancer parses gRPC requests and routes the gRPC calls to the appropriate target groups based on the package, service, and method.

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html