The feature is called <a href="https://docs.joinpeertube.org/admin/following-instances#instances-redundancy" target="_blank">"server redundancy"</a> and caches your most popular videos to help serve additional viewers.
<a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/install-any-os">Tu znajduje się instrukcja instalacji</a> (tylko po angielsku).