Man pages matching name pthread_spin_unlock in section 3:

pthread_spin_unlock.3.en	debian 10 / manpages-dev
pthread_spin_unlock.3.en	debian 11 / manpages-dev
pthread_spin_unlock.3.en	debian 12 / manpages-dev
pthread_spin_unlock.3.ru	debian 12 / manpages-ru-dev