Man pages matching name curlopt_upkeep_interval_ms in section 3:

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