Man pages matching name curlopt_chunk_bgn_function in section 3:

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