I'd always take applications that aren't entirely open source with a pinch of salt... I've always used FireFox combined with uBlock Origin.
It's like looking in the mirror... or at least from what I can remember when I did last look in a mirror. Ha!
I was thinking about this and wondering why DDG say they want to keep some of their source code private to maintain a competitive edge. Further, why do they need to advertise on TV if it isn't a commercial operation and how do they make their money? So it appears they do have online advertising and I quote from wikipedia:- "DuckDuckGo earns revenue by serving ads primarily from the Yahoo-Bing search alliance network (n.b. it's doesn't use google). As a privacy-focused search engine, the ads served on DuckDuckGo are based on keywords and terms of the search query. As of April 2024, DuckDuckGo also makes money from subscription fees paid to access Privacy Pro.