From pub.dev
"Q：Dart already has image compression libraries. Why use native?

A：For unknown reasons, image compression in Dart language is not efficient, even in release version. Using isolate does not solve the problem."

I have just tried isolate.run() method to keep imagecompress outside of the main threat.

Unfortunetely, it is not successfull.

For isolate, you need to write your own code and sure about the scope.

Flutter image compress is doing its job at the native side.