For Windows, "native" would be the classic Win32 UI "common control" elements from "Comctl32.dll"[0] that is directly used by older GUI frameworks such as Windows Forms. Those map to classic Win32 API CreateWindow(L"BUTTON", ...). In contrast, the newer frameworks of WPF and Xamarin Forms and Qt Quick "paints controls on a canvas" which are not "native" and makes every app UI look different instead of standardized "look & feel" of common controls.
But others include custom-canvas painting UI objects as "native" -- as long as it's not Electron.
[0] https://learn.microsoft.com/en-us/windows/win32/controls/com...