Thanks for the reply, @Rugby
I’ve confirmed that the share works across multiple MacBook Pro machines. I just can’t get Roon to see it, or to even accept it as a legitimate target.
If you re-read my post: (Currently, I backup to two SSDs attached via USB to a Roon Nucleus+, but a future core-machine upgrade will not allow me to write to attached USB devices.)
I will not always be using the Nucleus+, and am trying to get things sorted before the new arrival.