@dserber I’m not sure of a way to do this client side, but you could do this using two “Make Changes to a Thing” actions to obtain that list. For example, let’s say you have three “List” things (List 1, List 2, and List 3), and each List has an “Items” field (type: Item, list: yes).
To see which Items are not the same in List 1 and List 2 (i.e., exclude the same items in both lists), you can first set the value of List 3's list of Items to be List 1's list of Items merged with List 2's list of Items:
Then in the second action, remove the items that are the same in List 1's list of Items and List 2's list of Items from List 3's list of Items using “remove list” (list to remove: List 1's list of Items intersects with List 2's list of Items):
This way, List 3 would contain all of the Items which are found only in either List 1 or List 2, but not Items that are found in both List 1 or List 2. I think that should work, but let me know if not! 