They are installed in that the binaries are on the disk from the installation, but the cluster manager may not spawn the process since that service isn’t enabled, or may start them in a way that they’re only providing minimal services (in the case of the KV service).
Regarding others, examples would be the analytics and eventing services (and whatever we cook up next!). There are also one-time tasks like loading sample databases, which I believe are technically spawned by the ns-server component. That diagram just really covers the high level concept. The specific process hierarchy is more involved, but diagramming it probably wouldn’t help understanding the concept.