Man pages matching name parallel::prefork::spareworkers in section 3pm:

Parallel::Prefork::SpareWorkers.3pm.en	debian 10 / libparallel-prefork-perl
Parallel::Prefork::SpareWorkers.3pm.en	debian 11 / libparallel-prefork-perl
Parallel::Prefork::SpareWorkers.3pm.en	debian 12 / libparallel-prefork-perl