Man pages matching name plack::server::fcgi::engine::procmanager in section 3pm:

Plack::Server::FCGI::Engine::ProcManager.3pm.en	debian 10 / libfcgi-engine-perl
Plack::Server::FCGI::Engine::ProcManager.3pm.en	debian 11 / libfcgi-engine-perl
Plack::Server::FCGI::Engine::ProcManager.3pm.en	debian 12 / libfcgi-engine-perl