There is no such option on the Android Studio "build" menu on a Flutter project.
Instead you need to edit your android/app/build.gradle file to configure the signing settings. That way the APK or Appbundle will be automatically signed when you run flutter build apk|appbundle
To generate a keystore containing your signing certificate read this tutorial:
Then edit android/app/build.gradle adding these settings:
android {
// Other settings ...
signingConfigs {
release {
keyAlias '[YOUR ALIAS HERE]'
keyPassword '[PASSWORD TO YOUR KEY]'
storeFile '[PATH TO THE KEYSTORE YOU CREATED]'
storePassword '[PASSWORD TO OPEN YOUR KEYSTORE]'
}
}
// Some other settings.
defaultConfig {
// other configuration options
signingConfig signingConfigs.release
}
}
That way every build from now on will be signed with your certificate.
If you want to only sign release builds you can instead of adding the signConfig option to "defaultConfig" you can define the "release" build on the "buildTypes" section and add the signConfig there. That way only release builds will be