You can’t disable “whatever you want.” As the OP explains, in macOS 27 a “Siri AI” process stays running, always, doing who knows what, even if you turn everything off via the UI and CLI. If you know of a way to disable this, please post it because I’m sure many people would be interested in it.

As another example of what you can’t disable: I don’t wish to subscribe to Apple’s paid iCloud offerings. Yet there are several places in the UI both in macOS and iOS where there are non-removable ads for the service under certain conditions. For example, when your local storage fills up. Oh and now there’s a non-removable 20GB+ Apple LLM model now taking up space on my 256GB ssd. Thanks a lot Tim/John.