And plenty of well known companies have discovered that mastering two native stacks is still easier and cheaper in the long run, than mastering a "cross-platform stack" framework + dealing with leaky abstractions + build integration issues + having to master the native stack anyway.

Either go mobile Web, or native.

Yep, a good example is the element X rewrite

They use Jetpack on Android

https://github.com/vector-im/element-x-android

And SwiftUI on iOS

https://github.com/vector-im/element-x-ios

But both use the same underlying Matrix Rust SDK

https://github.com/matrix-org/matrix-rust-sdk

So they share the core part of the app between platforms, but everything user facing is native