I run Kubuntu which runs KDE apps and Plasma desktop and as such, has a native browser called Falkon which is based on QtWebEngine which is a stripped down version of the Chromium Core.
Qt itself https://en.wikipedia.org/wiki/Qt_(software)#History_of_Qt
(Is a widget toolkit for creating graphical user interfaces as well as cross-platform applications that run on various software and hardware platforms such as Linux, Windows, macOS, Android or embedded systems with little or no change in the underlying codebase while still being a native application with native capabilities and speed.)
https://en.wikipedia.org/wiki/KDE_Plasma_5#Software_architecture
Kubuntu with the Plasma desktop which is written in Qt so Qt is the closest thing to an OS rendering engine for this and many other Linux desktops. It’s fast and efficient and works with most Operating systems including mobile. I would think it would be a good choice for duckduckgo to use and would save them some work.
This 7 year old Thinkpad screams with Kubuntu/Plasma. Granted it has good specs for it’s age but it’s the fastest Linux I’ve ever used on any machine. I just stuck it on a few older laptops here in the past week as I plan to sell them. Replaced Lubuntu on one and it’s considered a light version of Linux but Kubuntu/Plasma is fancier and faster. I do need to upgrade RAM on a couple of them because 1GB just isn’t squat. One can be bumped up to 4GB and the other 8gb.
It will be interesting to see what they come up with and see if they even bother with a Linux version. Seems they could use Qt for most anything and have most Linux covered that way.