Man pages matching name mongoc_find_and_modify_opts_append in section 3:

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