Man pages matching name curlopt_rtsp_client_cseq in section 3:

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