I'm using both dev and latest canary....PIP absent on dev and works only on some websites in canary (like youtube). It's not working for most of the websites like reddit neither on dev nor on canary version. "Save video as" is not present on either of those
Picture in Picture (PiP) is only in the latest versions of Canary, but should be in the next Dev channel update, @Deleted. You are correct, PiP only works when the video is in an HTML5 video element. Many sites put their videos in other HTML elements such as a video player class inside a div element.