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.
Edit: honestly I assumed it had something to do with Google protecting themselves from image piracy shit
mp4 is a video format, the key differences with animated images being autoplay, looping and maybe transparency.
The point is the browser just plays the mp4 with autoplay and looping and then people call them GIFs when they aren’t. The only time you are looking at an actual GIF file is when the quality is atrocious and the colors are messed up because it needed to be dithered.