Counterpoint: Qt has done a terrible/non-existent job of this for iOS. Qt/QML apps look and feel pretty native on MacOS, and Qt & Qt Quick controls on Android devices look very close to Android native, but they've barely even attempted to implement iOS-looking controls. (It's bizarre how little interest they seem to have in supporting iOS. I don't know if it's because iOS doesn't have the styling APIs they need or what.) There is a third-party framework that partially addresses iOS issues (https://v-play.net/qt), but that's not an ideal solution.

For some applications (including the one I'm currently working on), you can get away with having nearly the same UI on Android and iOS, with just a little extra work to (for instance) give iOS users a more native-feeling navigation experience.

In regards to Flutter, I'm not sure if it's reasonable to expect the Flutter project to do a better job simulating native iOS widgets than Qt has been able to.