Animated WebP images are not supported. The error message is misleading (test file):
Not a valid file type: please upload a bmp, gif, jpeg, png, or webp file.
Feature request: Improve upload error message for animated WebP images, e.g.:
Animated WebP images are not supported.
(Note that animated PNGs work fine, e.g. https://i.sstatic.net/EXLLfEZP.png)
webp
tonon-animated webp
in the original message.static webp
to save a few bytes (I used to do some challenges in CodeGolf.SE)