Man pages matching name gnutls_dh_set_prime_bits in section 3:

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