Well, getting a hardware-accelerated blank buffer onto a screen to render video content is hardly the epitome of graphical user interfaces. VLC has very few and basic UI elements.

Jetbrains is a better example, using Java with Swing which is not a common choice. As seen from my other comment, I do think this is a good direction, but it ain't any more native than Flutter or for what it's worth an Electron app, none of these are "what the OS provide". FYI Jetbrains has to do quite a few platform-specific tweaks to make them better citizens on each platform.

VLC is not the example you're looking for. Written in Qt for desktop and their own libVLC wrapper for mobile. Yes, in the case of VLC, parent comment is right: you clearly see the issue. And a media player is a relatively uncomplicated piece of software, UI wise.