backup docker volumes, how to login as root?

[vesorit]

As written in the title, I want to do volumes backup. I know there exists other docker based solutions but they don't seem easy. With Duplicati I have other issues. How do I login as root via SFTP? If I put root in username, I get a timeout

Context: I downloaded the windows App and I connected the Windows machine to the remote server (that has Ubuntu)