Deliberate Omissions

Things a roadmap of this kind usually includes that were left out on purpose:

Omitted	Reason
GraphQL	Adds a query-language learning curve without teaching a Spring concept you’d otherwise miss
gRPC	Valuable, but only after you have several services. You’ll have two.
Reactive stack (WebFlux)	Java 21 virtual threads solve most of what WebFlux was for, and are far easier to reason about. Learn WebFlux later, if you get a real backpressure requirement.
Service mesh	Solves problems you get at 20+ services
Multi-region / multi-tenancy	Each is a roadmap of its own
Micro-frontends	An organizational solution to an organizational problem you don’t have

If someone tells you a backend roadmap is incomplete without these, ask them which user story requires it.