Man pages matching name mongoc_apm_set_server_opening_cb in section 3:

mongoc_apm_set_server_opening_cb.3.en	debian 10 / libmongoc-doc
mongoc_apm_set_server_opening_cb.3.en	debian 11 / libmongoc-doc
mongoc_apm_set_server_opening_cb.3.en	debian 12 / libmongoc-doc