>I have to convert a desktop app (actually written in python) to a web app. Since I respect the opinions of this group I was wondering what folks thought of the new
>google flutter. Flutter appears to be on the rise and is cross platform.

John,
a bit more info on the current app & "Web App" scope would have helped ;-)
Desktop with Python might involve Win, Mac & Linux
Web app can mean lots of things, even offline mobile capability like PWA!

If you mean "has to run in a browser in a more traditional way"
plus "will run for some years as based on python desktop app"
I'd look into CefSharp, which should have Python bindings by now as well.

With this you could aim to replace current GUI with something HTML/vue based
and add vue web/HTML frontend to some backend running most of your non visual current python...

Dotnet throws lots of weight behind unifying, so if total port is on the table,
might give better perf esp. on mobile with not everything under same umbrella as of now.

https://visualstudiomagazine.com/articles/2017/01/25/26-web-desktop-ui-tools.aspx
is 5 years old, but offer some leads.

No idea if the Neutronium stuff was used in production,
but IIRC you liked Vue.js half of my hint few years back a lot.

If "desktop" is Win only, the sciter stuff could be good/better tested/faster
to offer common HTML GUI on Win desktop with traditional Python based Web offer.

If installable PWA / mobile is a target, I'd look into something JS based with Vue as total replacement.
Flutter has Google behind it, but JS / PWA has as well from a larger coder base.

If a Python based mobile app is also planned, I'd port to mobile Python GUI
(Bee or Kivy) also running in desktop and redesign non GUI stuff into architecture
similar to Vue structures to reuse on a web backend.

Hope at least direction was correct
thomas