DDG uses Bing. Them blocking trackers except when they come from Microsoft (because of this search engine deal) is why I don't really care about using DDG.
You can use bangs to search on Google, but that's not the default.
Kagi is a Meta Search engine (it uses other search engines API e.g. Google, Yandex, Brave Search, Marginalia, ...) + it has its own (tiny) index, their own index mostly consits of their "Small Web" pages.