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

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