I was claiming (possibly incorrectly) that the FTPS in Duplicati exists but isn’t listed specifically as FTPS name. Perhaps you can resume trying to get it to work, or possibly there’s more help on it in the forum or on GitHub.
FTPS (also known as FTPES, FTP-SSL, and FTP Secure) is an extension to the commonly used File Transfer Protocol (FTP) that adds support for the Transport Layer Security (TLS) and, formerly, the Secure Sockets Layer (SSL, which is now prohibited by RFC7568) cryptographic protocols.
is from the link I cited, and Duplicati’s placement of encryption under FTP fits technically but is harder to spot.
Filezilla is, I think, quite good from a licensing view. Many of the fancy SFTP servers have license restrictions.
If you’re on a recent enough Windows 10, there is a beta version of OpenSSH-based client and server inside. This is a Windows port, but if you’re willing to run Windows Subsystem for Linux (WSL), more options open…
I’d note that the Windows port of openssh had some problems but fix might be known. No news from @DL38.