Man pages matching name posix_spawnp in section 3:

posix_spawnp.3.en	debian 10 / manpages-dev
posix_spawnp.3.en	debian 11 / manpages-dev
posix_spawnp.3.en	debian 12 / manpages-dev
posix_spawnp.3.fr	debian 12 / manpages-fr-dev