Flutter on the web is absurd: At least when I last checked, it's been rendering UI widgets into an HTML canvas by default, using its own low-level drawing library.
That sounds about as good of an idea as the old Java desktop GUI framework that used to (poorly) imitate native UI elements of Windows and macOS: Everything always looked three major versions behind and felt extremely janky.
I wouldn't care less if it worked in a performant way - in the end Flutter apps are using their own design (Material 2 / 3) - so rendering them in a Canvas is OK-ish.
The problem is that, on the web, the performance is extremely poor, so Flutter is still not worth being used there (IMHO).
That sounds about as good of an idea as the old Java desktop GUI framework that used to (poorly) imitate native UI elements of Windows and macOS: Everything always looked three major versions behind and felt extremely janky.