plugin no works but cache exists

The page is served via cache. If you are logged-in, you cannot see the cached version.

https://resmim.net/f/U7UnDw.png

Thank you so much for the speedy response. But in page speed insight why this page https://www.webseosem.it/wp-content/cache/all/ gives me good scores, instead the homepage (which should be identical) from low scores?

because your web-server is Ngnix and in nginx servers the cache is served via PHP so you get the following warning and it reduces the result.

https://resmim.net/f/7FqGFZ.png

There are solution without having to change server??

no, sorry.