Here is a list of all documented enums with links to the class documentation for each member:

encryption_algorithm : mongocxx::v_noabi::options::encrypt
encryption_query_type : mongocxx::v_noabi::options::encrypt
level : mongocxx::v_noabi::read_concern, mongocxx::v_noabi::write_concern
read_mode : mongocxx::v_noabi::read_preference
validation_action : mongocxx::v_noabi::validation_criteria
validation_level : mongocxx::v_noabi::validation_criteria
version : mongocxx::v_noabi::options::server_api