Thank you!
It looks okay to me too, but I would still recommend reverting back to the original .htaccess and testing that way.
From the screenshot I see that this file must exist for sure: https://www.rivesaltes.fr/wp-content/cache/asp/search1.css
Yet if you visit that URL you are greeted with a 404 page. That can only happen if the file really does not exist (but it does), or if there is a mod_rewrite rule of some sort which prevents the access, or maybe there is indeed a permission problem.
On the screenshot I see 750 as permission, that is not correct, it should be 755 at least, otherwise nothing can access those files. Please change the permissions to 755 recursively – including the cache, cache/asp/ and all the files within. I am 99% sure that will help.
If still no luck and the permissions are correct, then I suggest:
– Reverting back to the original .htaccess temporarily
– Reverting back all permalink settings temporarily
Then testing this URL until you start to see the file contents.