Just writing to confirm the experience of DuzAwe -- Docgyvers SSH plugin solves the issue of not being able to ssh into unraid v6.11.1 using key exchange.
I have a number of scripts that rely upon being able to ssh into unraid without a password. These worked fine until upgrading unraid. I tried all the fixes I could find in these forums without success. The unraid syslog.txt gave the error:
Authentication refused: bad ownership or modes for directory /
Weird, since I had already set permissions to 700 for the .ssh directory and 640 for the .ssh/authorized_keys directory as part of my troubleshooting the issue.
Anyhow, the plugin places an SSH icon in Settings > Network Services. Just open it and hit "Apply" without changing anything. Now everything just works.