Railway doesn't allocate fixed resources per instance that can be redistributed. Instead, you pay only for the resources your service actually consumes, and each service on the Hobby plan can scale up to 48 vCPU and 48 GB of RAM. If you're running a single service, it already has access to the full per-service resource limits, so there are no "unused" resources to reclaim from other slots.

each service on the Hobby plan can scale up to 48 vCPU and 48 GB of RAM. Cannot I get this used in 1 instance pls? anyways they are not used by me yet. Or is there is a way I can build my aplication to work across all instances and get the benefit of 48vPCU and 48GB ram allocation for one application?

The 48 vCPU / 48 GB figure is the total across all replicas combined, not what a single replica can access. On the Hobby plan, each individual replica can use up to 8 vCPU and 8 GB RAM, so running one replica gives you 8 vCPU and 8 GB, not the full 48/48. There is no way to pool the limits from unused replicas into a single one.