as you understand, we are not able to check your local host. Send me link
when you will have live site

the problem appears on localhost with fresh install of wordpress, the only 2 plugins installed are woocommerce and rehub frameworks, no theme modification

I gave you https://www.ecoles-du-web.fr/annuaire-formations-informatique-ecoles-du-web/ as an exemple

first of all, disable wp rocket lazy load for images on site. You can try
to disable wp rocket at all. If image will work after plugin disabling,
write to authors of wp rocket plugin

OK please go to : https://www.ecoles-du-web.fr/annuaire-formations-informatique-ecoles-du-web/ 

add the first three product to compare and click on the comparison icon on sidebar

product 1 and product 2 have webp featured image : they are not showing

product "livecampus" has jpg and it works

We are not able to check by screenshots. Direct link is required 

Hello

fresh install with latest WP, Woocommerce, Rehub ...

I notice that webp uploaded images are not showing in the sidebar when you click to compare products

(just before clicking "Compare", it is working in the comparison page)

see screenshot