Man pages matching name curlinfo_rtsp_client_cseq in section 3:

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