Man pages matching name mongoc_database_set_read_concern in section 3:

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