You can’t span a single replica set over multiple Kubernetes clusters using the Community Operator. You could do it yourself… but that’s not something we have specific guidance on.
(As a side note the Enterprise Operator does support multi-Kubernetes-cluster replica sets.)
As for how communication would work between members of the replica set on different Kubernetes clusters, we recommend using a service mesh for communication between clusters, but there’s a number of options to establishing the networking.