tl;dr - they use GeoIP to get geographic location to inform your search results and store search histories that are not associated with your IP address.
I think the article is a bit of an over-reaction. Compared to something like Google, DDG is a good alternative if you don't like the tracking and personalised results. (I've been using DDG as primary for years though so I may be biased)
I personally am happy for them to geo-locate me to a city of ~10 million if it means I get the "right" London and not the tiny one of 400K residents in Canada that is thousands of miles away from me when searching for something in London.
I think the problem is that they store «Your browsing history» as a holistic unit, which allows fingerprinting. A thought case: an actor could obtain their records, find your specific browsing history through the sites you visit (your fingerprint), and then also tie all your other searches to that. As a privacy focused search engine it’s concerning that they store individual search histories at all, even if not identifiable by IP.
I think the article is a bit of an over-reaction. Compared to something like Google, DDG is a good alternative if you don't like the tracking and personalised results. (I've been using DDG as primary for years though so I may be biased)
I personally am happy for them to geo-locate me to a city of ~10 million if it means I get the "right" London and not the tiny one of 400K residents in Canada that is thousands of miles away from me when searching for something in London.