Altium error: Un-connected Pin Constraint
I could not come up with a good direct answer to the question, but here's something to consider regarding this rule.

I've personally never used this rule and from reading the documentation it appears that it is redundant anyway:


  [This rule] detects pins that have no net assigned and no connecting tracks.


Basically, this rule will only find pins which have no net assigned to them. NC pins are very common, so you should instead use the Un-Routed nets rule on the PCB level.

Unconnected pins should be checked on the schematic level (run ERC before pushing changes to the PCB) and you can use No ERC to mark the pins that are unconnected by design.