Man pages matching name mongoc_session_opts_set_default_transaction_opts in section 3:

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