nginx 304 Not Modified (If-Modified-Since) - not found

[aderr]

Hello friends.
I am using the latest version of centos7 and the latest version of Vesta Сpanel. System is completely updated and no excess is installed.
All settings are standard, nginx,apache,php7.4.1 - I need to get 304 from the server,
And I get - if I do not enable nginx caching(in settings vestacp).

I check from this link. https://last-modified.com/last-modified ... e-php.html

adding to the settings nginx vhost
proxy_cache_revalidate on;
proxy_cache_background_update on;
proxy_set_header If-Modified-Since $http_if_modified_since;

separately or together these settings do not work, now I'm stumped.
is it really impossible to start a nginx cache and 304 Not Modified (If-Modified-Since) ?