Android
Change the Default Search Engine in Chrome auf Android
The address bar in Chrome doubles as a search box, and every unrecognized entry gets forwarded to whichever provider is set as the default search engine. On Android this defaults to Google unless you changed it before, and a Chrome update or a fresh app install can reset the choice back to Google without warning.
Switching the provider only affects address bar and new-tab searches inside Chrome. It does not change the assistant used for voice search or the engine used inside other apps that have their own built-in search.
To change it, open Open Chrome ➔ Open the menu ➔ Open the settings ➔ Tap on Search engine ➔ Choose a search engine. The list only shows providers Chrome has pre-approved or ones you have manually visited and searched with at least once, so a provider you want might only appear after you first search with it directly on its website.
If the setting keeps reverting to Google after every restart, a device policy from work profiles or a parental control app is usually forcing it, and the fix lies in that management app rather than in Chrome itself.