Apple Intelligence is training itself on the apps you allow by default. You can go to setings > siri > about siri, dictation & privacy, and switch that off if you wish. You'll have to do it app by app, one by one.
Mostly yes. And if it does require server-side processing, the data gets deleted after. This stance is totally different from other AI providers who make no such promises about data retention and/or using your inputs to train future models
It’s basically for allowing the voice assistant team to improve recognition by collecting references data, and for using usage behavior decide how to best sort search suggestions, when you like to use certain widget, and who should be prioritized in share sheet for certain apps at certain times. It’s pretty rudimentary.