On the Program Settings dialog, you need to specify which rsync.exe to use. There's also a button to download an rsync for Windows installer.
In the profile, you click on the Internet button for one of the two sides of the sync. Choose Rsync as protocol. You can securely connect via SSH or use rsync directly (unsecured). The unsecured connection can be used within a LAN or VPN, for example.
When using it via SSH, you need to have a client certificate and configure it on the Certificates tab sheet, as well as choose it on the Security tab sheet.
Because of limitations of the rsync.exe command line, some features are not working. For example, Syncovery cannot delete any files via rsync.
Because of rsync limitations, it is often better to use SFTP/SSH. It can do block level copying, too, and also it can get a recursive listing similar to rsync (on Unix/Linux servers). The recursive listing checkmark is on the second tab sheet of the Internet/FTP dialog.
Please see the following page for details about block level copying with SFTP:
https://www.syncovery.com/block-level-copying/The limitation with block level copying and SFTP is currently that it does block level for uploads only.