Go to Settings

Go to Search 

Scroll down to Search Shortcuts

Click on Add (under the box and next to Restore Default Search Engines)

Fill in a name in the field with Search Engine Name (For example : DDG noai)

In the field with URL with %s in place of search term fill in :

https://noai.duckduckgo.com/search?q=%s

Scroll up to the top of the page to Default Search Engine

and make DDG noai the default.

More information about DDG noai here :

https://duckduckgo.com/duckduckgo-help-pages/ai-features/about-noaiduckduckgocom

If you’d prefer an AI-free DuckDuckGo Search experience, start your searches on noai.duckduckgo.com instead of on duckduckgo.com. Searching on noai.duckduckgo.com works the same as search on duckduckgo.com, except all AI features are turned off and AI-generated images are filtered out of results by default.