Is Qt considered native when you use KDE and not native when you use GNOME? Is Qt 3 considered not native when you use a KDE release that uses Qt 4 under the hood?
I would say so. Just like GTK is native on GNOME but definitely not on Windows. "native" (to me) really just means whatever the system is designed for.
One could argue Win32 is still the de-facto GUI toolkit in Win10. Things like .NET Windows Forms and (non-WinUI3) UWP are actually rendered with Win32 common controls.
Indeed, but with some exceptions. .NET SWF shipped with extremely kludgy drawn clones of toolbars and menu bars instead of using the native ones (although the native ones were later exposed) and the result is that those particular controls on SWF apps did not age gracefully (DPI problems, system theme mismatch, scroll acceleration issues, etc). That’s the kind of thing Qt would also face with drawn components skinned to look like the real deal.