Flutter web: blank screen when 'webdev build'
I have a same issue but when I upload live server(host) it worked correctly. I am not sure but it can be about CORS, browser not allowed some source coming from outside of website so in local files has local source that means they are coming from outside the website as browser views. I think you should upload live server or local server.
My flutter web app was displaying a blank page / blank screen too...
Try running the following in the terminal:
flutter channel devflutter upgradeflutter run -d chrome
If it still shows you a blank page (because it's not reaching your local server for some reason) terminate the current server 'ctrl + c'.
Then run flutter run -d web and the terminal will provide you with a new local host url. Follow the link and refresh it once & you should see your app running.