So apparently Novel covers can be gifs and i never realized till now. Proof: https://www.novelupdates.com/series/dear-love/
Well gif do not need to be a "move" it is a compression which reduce the used color other like jpg reduce the pixel itself in on algorithm the biggest for me known misuse was on xerox-scaner which used for some years a wrong one and many copy till today have the nice effect in it see link .
It look grainy with compression and you not able to make gif as book cover, I like normal not moving cover