I don’t know what a .webp file is but I don’t like it. They’re like a filthy prank version of the image/gif you’re looking for. They make you jump through all these hoops to find the original versions of the files that you can actually do anything with.
mp4 isn’t generally for images.
Yes you can convert, it’s just that many existing tools may not presently support webp. If you just want a quick & dirty meme you can always screen cap.
The fun thing is
heifis actually effectively single frame of h.265 video because the amount of work that’s gone into making h.265 space efficient also happens to work really well for efficienct compression of individual frames of video aka images