Man pages matching name gnutls_transport_set_push_function in section 3:

gnutls_transport_set_push_function.3.en	debian 10 / gnutls-doc
gnutls_transport_set_push_function.3.en	debian 11 / gnutls-doc
gnutls_transport_set_push_function.3.en	debian 12 / gnutls-doc