CQRS is not a pattern that encompasses the whole application. It is a concept that builds on Domain Driven Design (DDD). And an important strategic concept of DDD is the so-called Bounded Context. In a typical application there are multiple bounded contexts, any of which can be implemented the way it makes sense. For instance User Management -> CRUD Invoicing -> CRUD Insurance Policy ...
CQRS (Command and Query Responsibility Segregation) é uma dessas siglas que nos deparamos e não conseguimos compreender completamente seu significado e utilização. O que é CQRS e como implementar?
O que é CQRS e como implementar? - Stack Overflow em Português
CQRS extends this concept into a higher level for machine-machine APIs, separation of the message models and processing paths. So CQRS is a principle you apply to the code in an API or facade. I have found CQRS to essentially be a very strong S in SOLID, pushing the separation deeply into the psyche of developers to produce more maintainable code.
Martin Fowler where CQRS might benefit you, and some where it will complicate things: CQRS fits well with event-based programming models. It's common to see CQRS system split into separate services communicating with Event Collaboration. This allows these services to easily take advantage of Event Sourcing. Having separate models raises questions about how hard to keep those models consistent ...
8 CQRS and CQS are like microservices and class decomposition: the main idea is the same ("tend to small cohesive modules"), but they lie on different semantic levels. The point of CQRS is to make write/read models separation; such low-level details like return value from specific method is completely irrelevant.