Most defualt devices come with operating systems like Windows, MacOS, and phone ROMs like iOS, OneUI (Samsung), Xiaomi (MiUI). They all have AI assistants. Alternative is to use custom operating systems or ROMs like:

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

Linux (PC) - Any distribution is fine, avoid Ubuntu or similiar 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 SearXNG (searx.space)

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

Youtube: NewPipe (Phone app) or FreeTube (PC) or invidious.io (Web)

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

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

Weather: openweathermap.org (Web)

Messaging and Calls: Signal (Phone app + PC)

Translators: libretranslate.com (Web)

You can block AI websites using hosts file method.