When flutter run is taking forever to initialize gradle it is probably due to network problem. Else, you might need to download gradle manually and install it. Downloading gradle manually is advisable especially if you are connected to extremely slow network.
If you can wait enough for gradle to finish downloading the problem should be solved automatically and on the next flutter run command it will be significantly faster.
To download gradle manually go to
you can also Try running
flutter run -v
and see which line takes long time