Out of curiosity, are you running the SFTP server on the same machine and Duplicati is running?
Also, does anything show in the Duplicati logs (either in the web interfaced or the C:\ProgramData\Duplicati\updates\Duplicati-crashlog.txt file)? You might want to try running the backup again while watching the Live log in Profiling mode (I find it easiest to do what with two browser windows - one on the log and one in which to
start the backup).
Oh, and you don’t have to use Docker for Minio.