Flutter : Could not build the precompiled application for the device. Error launching application on iPhone

Yes, I also got into this after upgrading to ios 14. So, first, add this to you podfile:

platform :ios, '9.0'

post_install do |installer|
  installer.pods_project.targets.each do |target|
    target.build_configurations.each do |config|
      # drop deployment target so it works with ios14
      config.build_settings.delete 'IPHONEOS_DEPLOYMENT_TARGET
    end
  end
end

and also run: flutter upgrade

For me, these 2 things fixed the problem.

If you want to simulate it immediately rather than taking care of the IDE issue generally, go to Tools -> Flutter -> Open iOS module in Xcode. But for a further solution, do a Flutter Clean, and remove the simulator from Xcode -> Window -> Devices and Simulators -> Simulators -> right click on your iOS simulator and click delete. Then add a new simulator from the bottom left corner “+” button in the same Devices and Simulators page you are on. Re run your app in flutter and it should be working.