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=”:

lemmy.world/…/e560537b-a944-4fd2-a0fe-f4abbad824a…

expanding the image and opening that image in its own tab gives me a url that links directly to the png:

lemmy.world/…/e560537b-a944-4fd2-a0fe-f4abbad824a…

just takes a little looking around the urls 99% of the time