Flutter is “native” if your definition of “native” apps are apps that compiled into native binaries. However, Flutter is not “native” if your definition of “native” apps includes apps that uses the native platform’s UI because afaik Flutter draw their own UI elements instead of using native UI elements, which is a deal breaker for some people.

The reverse can be said about React Native, where it’s not “native” because it uses javascript engine, yet it’s also “native” because it uses the native platform’s UI instead of rendering their own UI elements.