should be in the url for the file itself. this post, as an example, if I’m trying to save the thumbnail itself (from desktop browser), it gives me the link, with png hidden before the “format=”:
just takes a little looking around the urls 99% of the time. for mobile, I’m of limited help there. and I hope browsers support the container more directly in the future, because I agree that it isn’t as straightforward as it could be. I’ve also been seeing it pop up much more frequently in recent years, but that’s just me