Found solution:
sessionOptions.AddRawSettings("SshProt", "1");
https://winscp.net/eng/docs/rawsettings
https://winscp.net/eng/docs/library_sessionoptions
sessionOptions.AddRawSettings("SshProt", "1");
https://winscp.net/eng/docs/rawsettings
https://winscp.net/eng/docs/library_sessionoptions