Not correct me if I am wrong, but I thought undead (and Constructs) are immune to Fort saves (unless text says it affects objects).
Yet, Channel the Void doesn't say it affect undead (and Constructs) as though it was Fort (object) even though it should since they are immune to it as it is a Fort save.
Are you just supposed to assume it meant to affect undead even though it is a Fort save?
Or is this a goof up and needs to be errated?
Specific vs. General. This specifically can affect certain undead and constructs, thus it can affect those undead and constructs.
In essence, against undead and constructs for which the ability would apply, treat them as if the channel affected objects.
So constructs make a save as if their Constitution was 10, and undead make a save using their Charisma in place of their Constitution.
Or is this a goof up and needs to be errated?
Yes that summarises the archetype perfectly!