As the title says I want to merge some lists with the same columns together and then add a new column with the name of the list this item was extracted from. Is it possible to do this out of the box (with SharePoint online)? If it's not possible I'd create a new empty merged list and a workflow for the content lists, which just writes changes in the merged list. Here's an example of what I want to do:
List1:
item1
item2
List2:
item3
item4
MergedList:
item1 List1
item2 List1
item3 List2
item4 List2