Man pages matching name curlopt_unix_socket_path in section 3:

CURLOPT_UNIX_SOCKET_PATH.3.en	debian 10 / libcurl4-doc
CURLOPT_UNIX_SOCKET_PATH.3.en	debian 11 / libcurl4-doc
CURLOPT_UNIX_SOCKET_PATH.3.en	debian 12 / libcurl4-doc