I'm not sure what you do about it. I fell victim to this a couple decades ago trying to reconcile theme inconsistencies between GTK and KDE apps on my Linux desktop. It was so irritating, but for longest time I was overlooking that Windows at the time also had apps using different Windows UIs from different eras. IIRC Outlook actually had an XP scrollbar for the Inbox frame and a Win32 scrollbar in the Preview frame. Two different UI styles in different frames of the same window within one application.
Do you have any data to back this claim. From my experience, many big budget applications (at least on desktop) don't have native appearance. Eg. products by Adobe, Steinberg, Autodesk, JetBrains etc.
Also, Android has never pushed for unification of UIs. Use Material if you want because it's an alright design system, or write yours entirely from scratch.
React Native & Flutter look... Exactly how you want them to look. Unless there's a bug in Flutter's Material implementation, it'll be the same.
1) Difference between new latest Material You (aka material 3.0) and SwiftUI is smaller than Material 2.0 and UIKit - at least regarding look & feel.
2) I find old UIKit style quite boring same with older material 2.0. On the other hand SwiftUI and Material 3.0 looks more modern. There is rarely any iOS app that use native widgets without completely changing branding and styling.
3) Comparing to SwiftUI, new Material 3.0 feels more complete - there is more widgets and navigation choices. UIKit and SwiftUI is lacking in widget departments regarding: snackbar, bottom sheet, modal bottom sheet, navigation drawer, navigation rail, modal navigation drawer, cards, multiple dialog options.
I recommend to checkout and play with material 3.0 demo (just keep in mind this is web version- you will have even better experience when using native compiled version on mobile or desktop - web version of flutter could be better):
https://flutter.github.io/samples/web/material_3_demo/#/
4) Try web flutter gallery to see numerous app samples (more complex) and widgets
https://gallery.flutter.dev/#/
again even better to download mobile or desktop version that there is in play store:
play store: https://play.google.com/store/apps/details?id=io.flutter.dem...
macos dmg (.zip): https://github.com/flutter/gallery/releases/latest
I tried both macos flutter gallery and on iOS and surpassingly is pretty good these days and smooth and feel native - even text selection works these days, moving cursor with long press on keyboard space etc. Occasionally was more difficult to dismiss keyboard on iOS and back/next mouse keys or touchpad gestures didn't work on macOS flutter gallery. But overall I'm quite satisfied and surprised comparing how it looked 4 years ago.
This is what it looks like now in terms of performance if you want a demo https://flutter.gskinner.com/wonderous/