Cancel All Subscriptions and Asyncs in the componentWillUnmount Method, how?

You can use isMounted React pattern to avoid memory leaks here.

In your constructor:

constructor(props) {
    super(props);

    this._isMounted = false;
// rest of your code
}

componentDidMount() {
    this._isMounted = true;
    this._isMounted && this.getImage(this.props.item.image);

}

in your componentWillUnmount

componentWillUnmount() {
   this._isMounted = false;
}

While in you getImage()

async getImage(img) {
    let imgUri = await Amplify.Storage.get(img)
    let uri = await CacheManager.get(imgUri).getPath()

    this._isMounted && this.setState({
        image: { uri },
        ready: true
    })
}

A recommend approach to use Axios which is based cancellable promise pattern. So you can cancel any network call while unmounting the component with it’s cancelToken subscription.
Here is resource for Axios Cancellation