Quite likely the FTP data connection is blocked by a firewall or NAT. See
https://winscp.net/eng/docs/ftp_modes#passive
Can you retrieve the directory listing using any other FTP client running on the same machine as WinSCP? If you can, post its and WinSCP's verbose log files.

We want to connect Veeva Vault FTP according to https://developer.veevavault.com/legacyftp/,
and we're using WinSCP 6.1.2 with Windows 11.

Here is error message:

Disconnected from server
Could not retrieve directory listing
Error listing directory '/'.

The log is in attached.