What does this even mean. Chromium or Webkit are not “native” to an OS. OSs don’t magically include browser engines, its not a critical component of an OS either.

Most OSs do come with browsers preinstalled, but they are programs just like any other. You can remove Safari from macOS (albeit its pretty hard because root is read only and signed), you can remove Edge from Windows. In my desktop with Windows 10 the only browser I have is Firefox (not even Edge), does that make Gecko the “native” browser engine?

If anything, the native browser engine for Windows would be MSHTML from Internet Explorer.