Cannot find PIXI.Extract class in Pixi 6

API: https://pixijs.download/dev/docs/PIXI.CanvasExtract.html

However, as per the docs:

* app.renderer is undefined so cannot find the plugins

* PIXI.CanvasExtract is also undefined 

Environment

Pixi.js: 6.2.2

Use case: trying to take a screenshot of the app. It uses an opengl shader and dumping the canvas with `toBlob` yields no image.