How to setup the polish - covert image to Webp format

I setup with document and clear all cache. But the Image is still in the current format.
I open the devtool and check the response headers. I can not see the cf-polished attribute.
How does Polish work correctly? And how to test it?
Thank you in advance!

Do not activate Polish and Image Resizing simultaneously. Image Resizing already applies lossy compression, which makes Polish redundant.

We can see this listed in the first line under:

Can you make sure you do not have both enabled at the same time and see if your issue still continues?