Isn't such app best implmented with some cross platform framework like flutter? It has support for all major desktop OSes and at leqast the examples run very smooth.
The short version is that Flutter's lack of rich text editing solutions at the time made it a non-starter. It's a common problem in the Flutter ecosystem from what I've seen, there's often 0 or only 1 quality package for many "advanced" desktop use cases.
I've found that the GUI library I tried (fyne with go) was mobile-first, so some desktop things e.g. file-open dialogs didn't have the functionality I expected (the "dialog" was actually drawn within the same window as the application window). Flutter is mobile first too IIUC.
Outside of Qt, languages like rust and go don't have a good solid desktop GUI development option.
I do so with Rust also with the package flutter_rust_bridge which works great, I'm working on a mobile app that also simultaneously works on web and desktop when I tested it, even all the Rust parts.
Maybe in some cases, but I kind of doubt this statement in general. I just tried a Flutter demo from their official site and text selection doesn't even _work_ correctly.
https://flutter.github.io/samples/web/simplistic_editor/
I'll copy-paste a few lines of the example sentence, double click on one of the middle lines to start selecting by word (which it doesn't seem to even do), and then highlighting starts on the top line instead of the line I selected.
In general the flutter apps always feel janky and second-class to the platform they're on, because they never fully implement the exact behavior of each platform they run on.