Man pages matching name curlopt_sslcerttype in section 3:

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