To add to what Michael said: you should be able to do absolutely everything you can do today in, say, Kubernetes, using Service Weaver. While we try to do things like increasing the number of replicas automagically for you, you can absolutely disable this behavior and fix the number of replicas and/or use Kubernetes StatefulSets for example.
Roughly, Service Weaver aims to solve two problems:
1. Make distributed systems easier to write, e.g., don't write RPC code, don't worry about versioning, use language-native types.
2. Make distributed systems easier to deploy and manage.
If you prefer to preserve your existing deployment and configuration flow, you can still get tons of benefits from (1), and not rely on Service Weaver to handle (2) for you above.
As Michael said, there is 100% a way to achieve what you want even if replicas are dynamically scaled up and down, but in your case it may make sense to not rely on this Service Weaver behavior and fix the number of replicas yourself.