Man pages matching name curlopt_resolver_start_function in section 3:

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