Man pages matching name x509_name_add_entry_by_txt in section 3ssl:

X509_NAME_add_entry_by_txt.3ssl.en	debian 10 / libssl-doc
X509_NAME_add_entry_by_txt.3ssl.en	debian 11 / libssl-doc
X509_NAME_add_entry_by_txt.3ssl.en	debian 12 / libssl-doc