Default operating systems like Windows and phone ROMs like iOS, OneUI (Samsung), Xiaomi (MiUI) have AI assistants. Alternative is to use custom operating systems or ROMs made by other non-profit communities.

LineageOS (Android) (Without GApps) - Great option has support for lots of new and old devices.

Linux (PC) - Any distribution is fine, avoid Ubuntu and do your research.

Look for Open Source apps. I will give you list of some apps both for your phone and computer.

App Stores: F-Droid (Phone app) or Aurora Store (Phone app)

Browsers: Privacy Browser (Phone app) or LibreWolf (PC)

Search engines: noai.duckduckgo.com or searx.space

Email providers: Secria.me or Tutanota (Web + Phone App)

Youtube: NewPipe (Phone app) or FreeTube (PC)

Reddit: RedReader (Phone app) or old.reddit.com (Web)

Maps: Organic Maps (Phone app) or openstreetmap.org (Web)

Weather: Libre Weather (Phone app) or weather.com (Web)

Messaging: Signal (Phone app + PC)

You can block AI websites using hosts file method. Rename the file to "hosts"