They're making more than $100mm a year via ads and have been profitable since 2014 according to this Techcrunch article: https://techcrunch.com/2021/06/16/on-a-growth-tear-duckduckg...
They use Bing's ad network (or at least they used to) and don't expose any privacy details about their users, so advertisers can't target you based on demographic or psychographic information.