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

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