I am not really sure what you're talking about

RPC is "remote procedure call", emphasis on "remote", meaning you always necessarily gonna be serializing/deserializing the information over some kind of wire, between discrete/different nodes, with discrete/distinct address spaces

a client request by definition can't include anything that can't be serialized, serialization is the ground truth requirement for any kind of RPC...

a server doesn't provide "an object" in response to a query, it provides "a response payload", which is at most a snapshot of some state it had at the time of the request, it's not as if there is any expectation that this serialized state is gonna be consistent between nodes

Nothing stops me from implementing a Thrift or gRPC handler that uses a field from the request to look up an object in a hashmap and then call one of its methods with data from the request. But a distributed object system will do this implicitly on my behalf, so that the programmer’s perspective is like passing objects (by reference) over the network.