A lot of people saying this is a Chromium fork, but According to their blog, that’s not fully the case.
What’s under the hood
DuckDuckGo for Windows was built with your privacy, security, and ease of use in mind. It’s not a “fork” of any other browser code; all the code, from tab and bookmark management to our new tab page to our password manager, is written by our own engineers. For web page rendering, the browser uses the underlying operating system rendering API. (In this case, it’s a Windows WebView2 call that utilizes the Blink rendering engine underneath.)
I’d like to see if this makes an impact to the file size of the application since they don’t have to bundle all of Blink with the browser.