Man pages matching name curlopt_ftp_filemethod in section 3:

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