example/macos/ has been updated to enable App Sandbox by default, as well as to do ad-hoc signing (rather than disabling signing by default as in previous versions). Please see
for details on how the new security settings are configured and managed if you are building on macOS.
As the note at the end of the page says, feedback is welcome, as we'd like to iron out any issues before the future conversion of example/macos/ to a 'flutter create' template for macOS.
-Stuart