Hi Adrian,
In this case you can just remove the columns using the “Keep/remove columns”. Or, you can modify the iterated module/project to not return the extra columns. Finally, the proposed solution still works: Keep/Remove Columns by Condition
Generally speaking, I don’t see how columns can be removed using an expression. Such expression should be evaluated outside a dataset, but it should reference to column names inside the dataset. I don’t think it’s feasible.