tldr; After some research I found that including ?kbg=-1 to the url disables the AI feature. So, you can disable AI permanently using the following as your search engine configuration (which is available at least on Librewolf)

https://duckduckgo.com/search?q=%25s&kbg=-1

or you can temporary disable the feature by including -noai to your search query.

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Been using ddg for over 4 years and I feel it is getting slower these days. Or is it just me?

Startpage and other search engines loads fine. Also, I'm using Librewolf so the problem is not the cache.