Man pages matching name plack::middleware::proxy::addvia in section 3pm:

Plack::Middleware::Proxy::AddVia.3pm.en	debian 10 / libplack-app-proxy-perl
Plack::Middleware::Proxy::AddVia.3pm.en	debian 11 / libplack-app-proxy-perl
Plack::Middleware::Proxy::AddVia.3pm.en	debian 12 / libplack-app-proxy-perl