I’ve been using Royal TS for awhile and really like the functionality. For SSH, I use SSH keys that I have applied to the override and then only have the username set in the actual connection.
You should be able to try with public key and if that fails fallback to try a password and if not saved ask for one. That way you don’t run into the issue of the system not having the key installed and the system not working.
I understand I had to set either control or alt as the override but typically forget that and end up back here searching for the issue.
It would be nice if you included a Right Click option in the context menu that says… Connect (without overrides) or fix the ssh authentication to stick to things like putty.