Man pages matching name curlopt_happy_eyeballs_timeout_ms in section 3:

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