I don’t think I’ve seen a simple function that adds lists with duplicates. The most straightforward way I can think of is to initially add each element to it’s respective list AND a merged list custom state in the same workflow. This way you don’t need to merge, the list will always be there. But be careful to also add the options to edit/remove the item in the merged list as well.
There is a little hack i found which might help.
Use arbitrary text. Inside the arbitrary text put ‘List A , List B’. And then outside the arbitrary text use the :split by ‘,’ operator and the :each item converted to number.
This bypasses the need for :merged by operator which would remove duplicates.