I want to add filter on a workflow task list if the task is duplicated (same title with different ID) to show one item per task (show only the most recent one).
How to achieve this?
I don't think this is feasible out of the box. The only thing you could do is to group by Title (be sure to put index on title so performance is not degraded) and then display Descending by datecreated. This will not hide but will show latest task on the top.
Moreover if the tasks are duplicated maybe you need to refactor your workflow so that doesn't happen in first place.