Polish not converting images

I’ve enabled “Polish”, set to “lossy” and checking “WebP” and purge cache, however It seems that polish is not working. I have tested on this website: https://odoo-15-staging.klosterdrogerie.ch/all. The site is proxied by cloudflare. Here you can see that all files are served as png and not webp:

What did I miss in the configuration, or is there something blocking the converting?
Many thanks in advance for your help.

Because those images aren’t a cacheable file extension, they won’t be polished. The filename has to end in .png/etc, in order to be cached:


Once they’re cached with that extension, they can be polished:


Without the appropriate extension, they will not be Polished.