No, you are right. Flutter isn't really native since it uses Skia to render native platform look-alike components (as opposed to react-native which really use the platform)
The result is that everything will look and feel slightly off, as the recreation of native elements will never be quite perfect.
As I’d guess most people spend most of their time in Chromium browsers and electron apps probably a case to make that ‘native’ in the sense you imply is Chromium!
More than just off. Especially on iOS there is a ton of functionality in those native controls thats going to be very hard to replicate.