(oh, and QT supports 3d, on the web, on android, on ios, and on desktop, even on microcontrollers if needed)
And yes, Javascript's advantage has been that it was cross-platform pretty early on. Not particularly fast though, not even decades later.
And everybody keeps pointing out the same shortcoming: these frameworks let you share a lot of code, but mostly not the actual "View" (the V in model/view/controller) code, due to screen sizes, whether the UI can be resized, extra functionality (e.g. statusbar/notifications/...)
That's why new frameworks come out, because "why can't notifications on Windows work the same as on android?". "Why not just share UI?". Unfortunately, there's very good reasons they cannot work the same ... So a couple years in, these frameworks develop the exact same problems.
No it is not. Mobile apps are thriving. It is desktop apps that are niche now.
> ditching Flutter and using web tech for mobile too sounds like the better bet?
Quite possibly yes.
Either go mobile Web, or native.
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