@Mark Looking at @Gerard_Fernandez question again, I may have misunderstood his question. I didn’t realize he was in an Add/Edit situation, so I don’t think I have a solution for him.
As for a Visibility condition based on Relation/Lookup I think I may have set it up wrong. I was using a Multiple relation with a Lookup column against that Relation. I changed the Relation to be a non-Multiple single relation. The Lookup column I created against that relation now shows up under the list of columns that can be used as a condition under Visibility.
All-in-all, I learned something, but didn’t help anybody else.