As much as it would cost a native app. Say, on Mac, a plain AppKit app consumes 16-17 MB, gea consumes 18-20 MB, Qt consumes 25-35 (depending on whether you use QML or not) and Tauri consumes 58-60 MB. Tauri suffers a lot from all the WebKit dependencies, as its UI is not native but rather HTML rendered by WebKit.
Another data point: hello.c in GTK4 used over 100MB last I checked.
Don’t know about mac, but in windows qt hello world consumes about 10-15 mb. It is possible to optimise it to half of that. Fltk even goes lower to single digits. Crazy what fltk can manage to do even if creating simple utility apps like notepad or calculator.
A windows native app can be a few kilobytes on disk and use only as much memory as you give to set the stack size, so you might have to use actual numbers. Native can mean a lot of things and be extremely minimal.