For me, Flutter mobile isn't there yet either. I can see where it might be great for games with completely custom UIs, but I find the uncanny valley of pretend native controls a very uncomfortable place to be. Flutter could be a fantastic solution if it supported native controls and used JavaScript. I don't understand why Flutter's creators are so seemingly religious about Dart and reimplementing OS UI capabilities.
Sure, but most common mobile apps ARE completely custom UIs which insist on their own branding and look. The UI designers usually really hate if they have to use standard components and are unable to express themselves. Flutter just recognises that.
It's a bit more messy to do that with Android Framework, and because of that I see more of an argument for using Flutter there than on iOS. Jetpack Compose seems to be a lot better in that regard though.