That’s the case, yes – the UI runtime is Qt5 (which is rendered using low-level graphics APIs, so we class it as “native” – mostly in contrast to WebView-based UIs), and it’s the same API regardless of which platform you’re running on.
An example of native UI is libui or WxWidgets.
A similar thing happened to Android.
Windows 10 has several native GUI toolkits. The same thing happened in MacOS, which transitioned from Carbon to Cocoa.
If the widgets are drawn by a toolkit that isn't bundled with the OS, it's a non-native GUI. Of course, this isn't always a bad move.
But really, native look and feel only left on macOS. Windows lost its traditions around vista, linux never ever had one true way to do UI, and browsers almost exterminated everything else.