UniqueList Class in VBA
Just a couple of notes. The biggest of which is that I think you've misunderstood what VB_PredeclaredId does. It creates a default instance of the class. Which allows you to do things like this

UniqueList.Add someItem


Without declaring and setting a new instance of the class. It's a cool feature, but it's not what allows the list to be iterable and you don't need it here. The [_NewEnum] is what allows the For Each syntax. 

The Clear method doesn't need to Set list = Nothing. Drop that line and just set it to a new instance of Collection. 

Lastly, I find it really odd that you have a list with no way to get an element back out of the list. We can add and remove items, but not retrieve them. I would rethink implementing an Item method.