SyncBackSE and SyncBackPro both support FTPS, which is standard FTP using a secure SSL connection. SyncBackFree does not support FTPS.
SFTP is a different FTP protocol that uses SSH for a secure connection. Only SyncBackPro supports SFTP. However, it is still possible to access an SFTP server with SyncBackSE and SyncBackFree by using 3rd party software. For more details here:
An alternative to using FTP is to use SyncBack Touch. SyncBack Touch is a cross-platform file server. It lets SyncBackPro and SyncBackSE copy files to and from another device, e.g. Windows, macOs, Linux or Android device, over the network (LAN or Internet) just like an FTP server. SyncBackFree/Lite cannot use SyncBack Touch.
Simply install SyncBack Touch on the device you want to the access the files on and then create a profile in SyncBackPro/SE to use that device.
The advantages to using SyncBack Touch instead of FTP are that you can copy open/locked files, it's far simpler to set-up, doesn't have all the compatibility problems of FTP and doesn't require complex firewall/router configuration.