Another alternative: https://kivy.org
Nim can speed up up this framework.
The rapid adoption of Nim can pass through the mobile apps.
Flutter relies on the Dart VM's hot reload for development and Dart's OOP for GUI design.
And even if you could make it work, I don't see how you'd be able to convince Google.
I feel better with Bulma CSS Framework + Material Design Theme for Bulma, or Spectre CSS framework, or NimX.
I tried Kivy, all the screenshots looks awesome, but the feel of the use is kinda clunky, you can check Kivy IDE made on Kivy on Desktop feels weird and alien, feels too Tablet'y. For phone games is cool tho, but I will rater use Godot for that anyway.
Dart VM is redundant for Flutter. See for example Flutter for Go with no Dart (VM)
Go is only being used to implement the hardware abstraction layer for Flutter to work on the desktop. The application itself is still written in Dart and the resulting executable embeds the Dart VM. You can find the Dart files in the lib directory of the example apps.
Dart is integral to Flutter, as it is used in particular as the layout language for the UI, which relies on Dart-specific language features. While this can in principle be done in other languages, too, that would require a lot of porting effort, as the current codebase to implement that consists of hundreds of thousands of lines of Dart and C++.