Man pages matching name gnutls_fips140_set_mode in section 3:

gnutls_fips140_set_mode.3.en	debian 10 / gnutls-doc
gnutls_fips140_set_mode.3.en	debian 11 / gnutls-doc
gnutls_fips140_set_mode.3.en	debian 12 / gnutls-doc