When setting up Guacamole I had issues with connecting to the ubuntu machine via a ssh connection. The server simply said connection error.
Knowing very little about any of this, but it seems like Guacamole only supports ssh-dss and ssh-rsa, and both have been disabled in Ubuntu.
DSS was removed 8 years ago and it seems from my quick google that RSA has been deprecated, so hopefully Guacamole updates sometime soon.
In the meantime a workaround is adding “HostKeyAlgorithms +ssh-rsa” to the end of /etc/ssh/sshd_config on the Ubuntu machine and restart sshd. Note: I don’t have an understanding of the security implications of this, so use at your own risk