As neither gif nor webp are standard compliant formats for embedded covers, I think it is a vain attempt to get these displayed. If it works - fine. If it doesn't - that's the way it is.
Yeah, it would just be nice to be able to see the thumbnail somewhere while these files are on my PC, so I had to ask. In windows the files I embed these to don’t show thumbnails. So it’s a blank looking file everywhere except my music player. I’ll likely have to just use a tag field for a description or maybe the checkbox to denote animated artworks