Apple has sold computers with local voice input and command processing for more than 20 years, and iPhones have pretty much always had that feature (it was called “Voice Control” before Siri existed, and it was 100% local).
I’d argue that, for Apple, what they’ve started doing recently is processing commands in the cloud. The list of commands that are processed locally vs in the cloud has changed over time… and they did move most of it to the cloud several years ago when they bought a cloud based smart assistant startup and used it as the basis for a new an improved assistant on iPhone. But every year they remove the dependence on that and are going back to how it used to be with local processing. These days even when a command is processed in the cloud it’s often only part of a multi-step process where the majority of the work was done on device. And many everyday commands are done entirely on device.
For example if you ask it what the weather is, it’s entirely an on device command except for actually checking the latest weather report… and you can ask it what the temperature is “inside” which will check a sensor in your house and be entirely offline (if your home has a temperature sensor. There’s one built into Apple smart speakers and also a small but growing number of third party smart home products)