Don’t understand how it is supposed to work

I et up the plugin and everything appears finde, regenerated all images to begin with. Didn’t notice a diference. When I know go to the page and check and open a pic, it is always still a jpg. Maybe because the filesize was smaller than it would be with WebP anyway, but where can I find what the plugin did or didn’t do?

The page I need help with: [log in to see the link]