DDG uses Bing’s results. Bing has deteriorated less than Google but it’s also becoming worse every day.
It doesn’t use just bing anymore: https://duckduckgo.com/duckduckgo-help-pages/results/sources/
That page is pretty misleading, though: it’s mostly talking about ‘Instant Amswers’ which is its AI (presumably) paid partnership answer bot thing at the top of the results. Further down, it says: “Of course, we have more traditional links and images in our search results too, which we largely source from Bing.”
So, although they don’t use Bing exclusively, that’s where the majority of non AI-answer-bot stuff is coming from. And I’m guessing the AI is Bing/Microsoft powered anyway, although I can’t be sure.