Hi @Lr_Test_Demo,
I am not sure getting a blob from the canvas will work to grab an image.
Here is an easy way to do what you are trying to do, tested on Chrome:
// on init
var linkElement = document.createElement('a');
linkElement.id = 'link';
window.document.body.appendChild(linkElement);
// download method
var image = this.app.graphicsDevice.canvas.toDataURL('image/png');
var link = document.getElementById('link');
link.setAttribute('download', 'image.png');
link.setAttribute('href', image.replace("image/png", "image/octet-stream"));
link.click();