https://html.spec.whatwg.org/multipage/canvas.html#the-image-argument-is-not-origin-clean

The image argument is not origin-clean if it is an HTMLOrSVGImageElement or HTMLVideoElement whose origin is not the same as the origin specified by the entry settings object, or if it is an HTMLCanvasElement whose bitmap's origin-clean flag is false.

In particular, it doesn't check for ImageBitmap arguments, so the following doesn't taint the canvas:

createImageBitmap(crossOriginVideo).then(bitmap => ctx.drawImage(bitmap))