Security / privacy on device: Don’t use devices / OS you don’t trust. I don’t see what difference on-device AI have at all here. If you don’t trust your device / OS then no functionality or data is safe.
Security / privacy in the cloud: The take here is that Apples proposed implementation is better than 99% of every cloud service out there. AI or not isn’t really part of it. If you already don’t trust Apple then this is moot. Don’t use cloud services from providers you don’t trust.
Security and privacy in 2024 is unfortunately about trust, not technology, unless you are able to isolate yourself or design and produce all the chips you use yourself.