Man pages matching name curlopt_tcp_keepalive in section 3:

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