@_elena @stereo I'm a bit late, but yes, you're right. YunoHost disables root login by default if it maintains the file /etc/ssh/sshd_config (this is a setting during setup). The corresponding line is "PermitRootLogin no".
However, the YunoHost admin account that you've created during setup and that you use to log into the web interface is also the one that is allowed to use SSH. For example, if your admin username is called "elena", the command "ssh elena@..." should work.